Disaster incidence by hazard category, 1900–2005.
In 2007, the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) concluded that these same climate-caused hazards will continue to rise in frequency and severity well into the future.5
Floods constituted three of the world’s ten deadliest hydrometeorological disasters from 1900–2013, ranked according to number of people killed per nation.15 Table 35.1 shows the major hydrometeorological disasters that occurred from 1900–2013 and the number of fatalities associated with each event. All of these disasters occurred in developing nations, and all were caused by either floods or droughts.
The world’s ten deadliest hydrometeorological disasters, 1900–2013, ranked according to number of people killed per nation15
| Hazard | Country | Year | Number killed (in millions) |
|---|---|---|---|
| Flood | China | 1931 | 3.7 |
| Drought | China | 1928 | 3.0 |
| Flood | China | 1959 | 2.0 |
| Drought | Bangladesh | 1943 | 1.9 |
| Drought | India | 1942 | 1.5 |
| Drought | India | 1965 | 1.5 |
| Drought | India | 1900 | 1.25 |
| Drought | Soviet Union | 1921 | 1.2 |
| Drought | China | 1920 | 0.5 |
| Flood | China | 1939 | 0.5 |
During 1900–2013, floods also affected the highest percentage of people (43.56%) worldwide among all hydrometeorological disasters (Figure 35.2).15
Percentage of people affected worldwide according to each category of hydrometeorological hazard, 1900–2013.
During the past three decades from 1980 to 2011, there have been 7,009 climate-related disaster declarations worldwide, averaging 226 per year (Figure 35.3).16 Floods have comprised 3,455 (49%) of these disasters.
Number of climate-related disasters around the world, 1980–2011.
According to the U.S. National Oceanographic and Atmospheric Administration (NOAA), “In most years, flooding causes more deaths and damage than any other hydrometeorological phenomena. In many years it is common for three-quarters of all federally-declared disasters to be due, at least in part, to flooding.”18
Parts or all of over 20,000 communities in the United States are subject to a substantial flooding risk. Approximately 7% of the nation’s land area, an area almost as big as the state of Texas, is subject to severe flooding.19 In the United States, floods cause as much as 90% of the damage from disasters (excluding droughts).20
Direct economic losses from the 1993 Great Midwestern U.S. floods surpassed $10 billion USD.21 Estimated flood damage as a result of the 1998 floods in central Texas was approximated at $900 million USD, including damage to 12,000 homes, 700 businesses, and to public property.22 In the late summer of 2005, flooding after Hurricane Katrina caused more than $200 billion USD in losses, constituting the costliest disaster in U.S. history to that date.19 Flood-related losses associated with Hurricane Sandy in 2012 are estimated at $25 billion USD.23 Trends toward increasing population density near coasts and in floodplains suggest a higher probability of future catastrophic flood disasters. The current trend of climate change is projected to have an impact on the frequency and severity of floods worldwide.5,24 Munich Re, a re-insurance company and member of the UN Environment Programme’s (UNEP) Finance Initiative, has been compiling annual records since the 1970s on the cost of disasters. In 2002, Munich Re reported that rain intensities reached unique values worldwide. The report estimated that during 2002, floods caused 42% of worldwide fatalities, 66% of the economic losses, and 64% of insured losses.24
Floods are also notable in their capacity to affect extremely large groups of people. The largest single flood during the past century is estimated to have impacted nearly 239 million people.15 Table 35.2 lists the world’s ten largest floods from 1900–2013, ranked according to number of people affected.15
The world’s ten largest floods (1900–2013) ranked according to number of people affected15
| Country | Year | Number affected |
|---|---|---|
| China | 1998 | 238,973,000 |
| China | 1991 | 210,232,227 |
| China | 1996 | 154,634,000 |
| China | 2003 | 150,146,000 |
| China | 2010 | 134,000,000 |
| India | 1993 | 128,000,000 |
| China | 1995 | 114,470,249 |
| China | 2007 | 105,004,000 |
| China | 1999 | 101,024,000 |
| China | 1989 | 100,010,000 |
Public Health Impacts of Flood Disasters
Public health impacts of flooding include damage to homes and consequent displacement of occupants, infectious disease exacerbated by crowded living conditions and compromised personal hygiene, contamination of water sources, disruption of sewage service and solid waste collection, increased vector populations, injuries sustained during clean-up, stress-related mental health and illicit substance use, and death (Table 35.3).25
Relative degree of expected public health impact after a flood
| Impact | Degree |
|---|---|
| Drowning mortality | High income nations – Few Low income nations – Can exceed 100,000/event |
| Epidemics | Can occur in low-income nations |
| Need for trauma care | Rare |
| Loss of clean water | Can be widespread |
| Loss of shelter | Can be widespread |
| Loss of personal and household goods | Can be widespread |
| Permanent population migration | Rare |
| Loss of routine hygiene | Can be widespread |
| Loss of sanitation | Can be widespread |
| Disruption of solid waste management | Can be widespread |
| Public concern for safety | High |
| Increased pests and vectors | Can be widespread |
| Loss and/or damage of healthcare system | Can be widespread |
| Worsening of existing chronic illnesses | Can be widespread |
| Toxic exposures | Possible |
| Food insecurity | Can occur in low-income nations and remote islands |
Loss of Safe Water and Adequate Sanitation
During the 1993 Great Midwestern U.S. floods, 9% of the population in the state of Iowa suffered a complete loss of the public water system. Twenty-nine counties in Iowa (representing 37% of the population) reported flood damage to water systems, and thirty-one counties (with 35% of the population) reported flood damage to sewer systems.26
Food Insecurity: Crop Losses and Disruption of Food Distribution
Generalized food shortages severe enough to cause nutritional problems usually do not occur after disasters, but may arise among low-income nations in two ways. Food stock destruction within the disaster area may reduce the absolute amount of food available, or disruption of distribution systems may curtail access to food, even if there is no absolute shortage. For example, food security has become a major issue in Southeast Asia, as it has been difficult to deliver food supplies to flood-affected areas.27 In addition, severe damage to agricultural land and livestock affects those who rely on these forms of food production, with main food crops severely damaged, along with losses in livestock and poultry.28 This puts many people out of work, placing a financial strain on the economy and on many businesses and families.27
Flooding and sea surges can damage household food stocks and crops, disrupt distribution, and cause major local shortages. Food distribution, at least in the short term, is often a major and urgent need, but large-scale importation/donation of food is usually unnecessary.29 One notable exception occurs when remote low-lying islands are flooded by seawater to an extent that island aquifer becomes brackish and agricultural land becomes salt-contaminated so that it can no longer support gardens for the next several years. Such an inundation event occurred in the U.S.-associated Pacific island nation of the Federated States of Micronesia during March 2007 and resulted in a loss of food security sufficient enough to warrant a federal disaster declaration.30,31
Loss of Shelter and Population Displacement
Floods displace literally millions of people. Displacement is a key risk factor for morbidity and mortality among disaster-affected populations. It creates additional risk for vulnerable populations (see Chapter 10).
The disruption caused by this displacement and the new focus on uncertainties of recovery rather than their previous normal daily routines are a source of high stress. The psychological stress that people suffer after a flood is related to not only reconstruction of their home but also “everything it stood for” in terms of memories and sentiment.32–34 Flood survivors personally identify with damage and destruction of their homes and personal possessions. Many claim their most devastating losses are the personal possessions that “cannot be replaced.”32
Misdirected or misguided settlement solutions may increase and prolong the risk of morbidity and mortality among displaced populations by providing shelter below internationally accepted standards for space, nutrition, food, clean water, safety and security, sanitation, hygiene, and access to medical care.35
Individual household shelter solutions can be short or long term and subject to the level of assistance provided, land-use rights or ownership, availability of essential services and social infrastructure, and opportunities for upgrading and expanding dwellings. Existing shelter and settlement solutions should be prioritized. If sustainable, involved populations should be allowed to return to the site of the original dwellings. Affected households who cannot return to the site of the original dwellings should be permitted to settle independently within a host community or with host families, whenever possible. Temporary camps and mass shelters should only be used as a last resort, that is, for persons who cannot return to flood-affected areas and cannot settle independently within a host community. Research shows that providing increased social support can significantly lower illness burdens after disasters.35
Toxic Chemical Exposures
The mobilization of chemicals either from storage (e.g., underground fuel tanks, pipelines, hazardous landfill sites, and wastewater lagoons) or by remobilization of chemicals already in the environment (e.g., pesticides, dioxin in river/canal sentiment, runoff from roads and bridges, overloaded sewers, and acid mine drainage) has occurred during floods.36 These chemical hazards are more likely to materialize when industrial and agricultural areas are submerged underwater.4 One 2004 review identified epidemiological evidence for flood-related adverse health effects following chemical exposures to carbon monoxide, pesticides, agricultural chemicals, dioxin, volatile organic carbons, heavy metals, cyanide, acid waste water, sulfides, and cadmium.36
According to local fire department records, 1,200 homes in Grand Forks, North Dakota, affected by the 1997 Red River flood reported problems with fuel oil spills ranging from 190 to 985 liters. Experts from the U.S. Environmental Protection Agency (EPA) conducted a study of thirty-four homes approximately 1 year after the flood occurred. Six homes (17.6%) still had measurable hydrocarbon vapors that were considered a serious health threat. The homeowners were advised to move or undergo major structural work to replace contaminated structures.37
Toxic Mold Exposures
In 2004, the U.S. Institute of Medicine (IOM) published a review of the literature regarding health outcomes related to damp indoor spaces. The findings of this report indicate that indoor environmental conditions and personal practices provide mold exposures that may expose residents and remediation workers to risk of negative health effects.38
Molds were identified as a potential public health concern arising from the 1993 Midwestern floods.4 Visible mold growth was found in 46% of homes inspected after flooding caused by Hurricane Katrina.38 Aspergillus and Penicillum species were the predominant fungi identified, both indoors and outdoors. Although interpreting the significance of measures of airborne mold toxins is complex, indoor air levels were markedly elevated and usual indoor/outdoor ratios for mold were reversed, that is, indoor levels of mold toxin were higher than outdoor.38,39
Among the residents interviewed, two-thirds quickly identified particulate respirators as appropriate and necessary respiratory protection for cleaning of mold. Of those who had cleaned up mold, two-thirds did not always use appropriate respirators. Among persons who self-identified as remediation workers, 95% thought mold causes illness and 85% correctly identified particulate filter respirators as the appropriate protection for cleaning up mold. However, 49% of remediation workers had not been fit-tested for respirators and 35% of the same group reported that they did not always use respirators.38 These findings suggest that a significant proportion of disaster-affected residents and remediation workers may be exposed to potentially hazardous levels of mold. Reasons for this include a lack of understanding of the need for or lack of access to personal protection, or a lack of compliance despite recognition of the need for and availability of protection.38
Disruption of Healthcare Services
Flooding may directly damage healthcare entities or it may hinder public access to these facilities by disrupting transportation routes. During the Great Midwestern U.S. floods, five of the ninety-nine counties representing 14% of Iowa’s population reported closures of primary care physician offices.26 In 2008, months of heavy rainfall and rampant flooding in Mozambique, Zambia, Zimbabwe, and Malawi reportedly restricted access to healthcare facilities among patients as well as drug and supply distributors over a very large area of southern Africa.40
Floods have a substantial impact on the operation of most emergency medical services systems. The primary effect often results from disruption of usual transport routes due to water. Data concerning air transport in flooding collected during Hurricane Floyd in the United States demonstrated a nearly 650% increase in helicopter utilization for emergency medical services transports in the affected areas.6 In most flood-related disasters in the United States approximately 0.02–2% of flood survivors require emergency medical attention.41
The Great Midwestern U.S. floods presented multiple challenges to the six metropolitan medical centers in Des Moines, Iowa, when these hospitals lost all public utilities. Healthcare leaders cancelled elective admissions and diverted non-emergency clinical services to alternate facilities. They identified and implemented ancillary resources in order to maintain essential operations. Hospital managers initiated non-routine methods for infection control, sterilization, housekeeping, and food preparation. Planners implemented extraordinary measures in order to maintain adequate amounts of water for laundry, fire protection, cooling, instrument sterilization, renal dialysis, physical therapy, and dietary services.42
Disruption of Public Services
During the Great Midwestern U.S. floods, eight counties in Iowa (24% of the state population) reported interruption in public health services (e.g., supplemental food programs and various clinics like those for vaccinations and for treatment of sexually transmitted infections). Ten counties (15% of the population) reported at least one non-operational public sewer system.26
Power outages are a common impact of flood disasters. Power outages not related to flooding have been associated with outbreaks of diarrheal illness.43 The disruption of public access to refrigeration may impact food and also drug safety. For example, life-sustaining medications such as insulin require properly controlled refrigeration in order to remain efficacious.
In addition to flood water disruption of solid waste management services, floods may also generate a large amount of additional solid waste. The degree of extra sold waste generation is proportional to population density and extent of area flooded.44
Flood Myths
Misconceptions regarding the need for large-scale public health interventions related to communicable disease prevention and control are common after flood disasters. Even after learning that there is little scientific basis for implementing such programs, public officials are often tempted to carry through with such plans, sometimes rationalizing that “at least we feel like we’re doing something.” However, implementing these programs at the time of disasters is often counterproductive and diverts limited personnel and resources from other relief tasks.6 In addition, these interventions are not without health risk. Officials should therefore carefully weigh the risk versus limited proven benefit (Box 35.1).
Flood Myths
Mass Vaccination in Absence of an Outbreak
There is often a public demand for typhoid vaccine and tetanus toxoid after floods despite the fact that no epidemics of typhoid or tetanus have occurred after floods in the United States. In some cases, misinformed officials make recommendations for a “flood shot.” These recommendations have included immunizations for hepatitis, typhoid, and tetanus.
Mass tetanus vaccination programs are not indicated. Management of flood-associated wounds should include appropriate evaluation of tetanus immunity (and vaccination if clinically indicated) just the same as at any other time.6
Some response agencies have recommended typhoid and hepatitis immunization for individuals about to deploy to a flood disaster. This occurs despite the fact that it takes several weeks for antibody to typhoid to develop, and even then vaccination provides only moderate protection.6 Hepatitis immunization requires a series of vaccinations that are months apart. Thus, in both cases, immunization can create a false sense of security and may contribute to neglect of basic hygiene.
Large-Scale Mosquito Control in Absence of an Outbreak
The public and well-intentioned public officials often expect to implement large-scale mosquito adulticide in the midst of a flood disaster, despite the presumed low risk for mosquito-borne arboviral disease after flood-related disasters in high-income countries.61 Besides unnecessarily diverting human, fiscal, and logistical resources, the action also increases the possibility of chemical exposures to workers and the public. Vector surveillance is adequate and should be used to guide any consideration of mosquito control.61
Fatality Management
The public is often concerned about the danger of disease transmission from decaying corpses. Responsible health authorities should be aware that health hazards such as epidemics associated with unburied bodies are minimal, particularly if death resulted from trauma or drowning (see Chapter 23). It is far more likely that survivors will be a source of disease outbreaks.29 Mass graves are not necessary when considered solely to prevent the spread of disease caused by mass fatalities. For flood disasters, normal funeral ceremonies and practices should be respected and maintained whenever possible.
Flood-Related Morbidity and Mortality
Flood-Related Mortality
Drowning is the main cause of deaths due to floods. From 1900 to 2011, extreme weather disasters killed over 19 million people and affected nearly 3.2 billion people worldwide.15 Floods comprised nearly 34.6% of these disaster-related deaths.15 Floods portended the second highest mortality rate among the top ten disasters for each category of extreme weather hazard worldwide from 1900–2013 (Figure 35.4).15
Mortality Rate among the Top Ten Disasters per Hydrometeorological Hazard Category, 1900–2013.
Floods constituted three of the world’s ten deadliest hydrometeorological disasters (1900–2013), ranked according to number of people killed per nation (Table 35.2).15 Seven of these floods occurred in China. All ten occurred in low-resource countries.15
Floods are the number one non-terrorist disaster in the United States in terms of lives lost and property damage.45 Over a 25-year period prior to Hurricane Katrina, floods killed about 140 Americans and cost $6 billion USD in property damage each year. In the United States, the most common cause of flood-related deaths is drowning.19
“The number of deaths associated with flooding is closely related to the life-threatening characteristics of the flood (rapidly rising water, deep flood waters, objects carried by the rapidly flowing water) and by the behavior of the victims.”46 The most readily identifiable flood deaths are those that occur acutely from drowning or trauma, such as can happen after being hit by objects in fast-flowing waters. The number of such deaths is determined by the characteristic of a flood, including its speed of onset, depth, and the extent of flooded area. Information on risk factors for flood-related death remains limited, but men appear more at risk than women. In high-income countries most deaths are due to drowning and, particularly in the United States, are vehicle related.4,47 The most likely group to drown in their own homes are the elderly.47
Flash floods are the number one cause of flooding deaths.4 Flash flooding is the leading cause of weather-related mortality in United States.26 In general, higher mortality rates are observed in flash flood incidents, examples of which occurred in Puerto Rico in 1992, Missouri in 1993, Georgia in 1994, and Texas in 2001 when heavy water runoff inundated communities with great immediacy and intensity.6,25,48 The majority of flood-related drownings occur when a vehicle is driven into hazardous flood waters.4,22
The power of water, especially moving water, is astounding. For example, ‘‘Two feet [0.6 meters] of water will carry away most automobiles. The lateral force of a foot [0.3 meters] of water moving at 10 mph [16 km/h] is about 500 pounds [227 kg] on the average car. And every foot [0.3 meters] of water displaces about 1,500 pounds [680] of car weight. So two feet of water moving at 10 mph [16 km/h] will float virtually every car.’’49
During the 1998 floods in central Texas, twenty-four of the twenty-nine deaths directly related to the storm were caused by drowning. Of those twenty-four drownings, twenty-two (92%) with known circumstances occurred because the vehicle was driven into high water. These deaths occurred in sixteen separate incidents, some with multiple deaths. Of the sixteen water-crossing incidents, eleven (69%) occurred at locations known to reporting authorities to have a history of flooding; ten (63%) involved trucks and/or sport-utility vehicles.22
Prior to the implementation of early warning, evacuation, and shelter systems, drowning from hurricane storm surge accounted for an estimated 90% of cyclone-attributable mortality in both high-income and low-income nations.4 Approximately 8,000 people died from flooding in 1900 after a large hurricane struck Galveston, Texas. In 1928, 1,836 people died from another hurricane storm surge around Lake Okeechobee in Florida. Large storm surge associated with powerful hurricanes was believed to be the cause of most of these deaths.
Storm surge drowning deaths have markedly decreased in high-income nations due to improvements in population protection measures.50 One notable exception is that more than 1,300 deaths were attributed to Hurricane Katrina, most of which occurred as a result of flash flooding caused by catastrophic levee failure, making 2005 the third deadliest year in U.S. history for flood deaths to that date.51
Flood-Related Morbidity
Poverty and Flood-Related Morbidity
Poverty is a key risk factor for human vulnerability to flood disasters. The correlation between poverty and morbidity is seen clearly during flood disasters. Low-income populations within a given society often dwell in locations at higher risk for flooding and have fewer resources available for response and recovery. Rarely, if at all, are any resources available to prepare for or mitigate flood disasters. High-income populations within a society possess a much higher level of resilience and availability of resources that can better afford more cost-effective risk reduction measures. Diseases normally endemic to a given population are typically exacerbated as a result flood disasters. As a result, low-income nations have a higher incidence of flood-related outbreaks of infectious disease, such as leptospirosis, typhoid, malaria, and cholera. High-income nations tend to suffer few flood-related outbreaks, but instead have a higher proportion of flood-related non-communicable diseases, such as injuries, mental illness, cardiovascular disease, and chronic obstructive pulmonary disease.
Causes of flood-related morbidity reported in high-income nations during the first 6 weeks after the disaster are frequently equally divided between injuries and illnesses. Injuries commonly include sprains/strains, lacerations, and abrasions. Many of these injuries occur later during the clean-up phase rather than immediately during the flooding. Communicable and noncommunicable diseases cause similar numbers of flood-related illnesses in high-income nations.26,50
Communicable Diseases and Flood-Related Morbidity
The relationship between disasters and communicable diseases is frequently misconstrued. The risk for epidemics is often presumed to be very high in the disaster aftermath. The risk for outbreaks after disasters is often greatly exaggerated by both health officials and the media.29 The risk of infectious diseases after flood-related disasters is often specific to the event itself, and is dependent on a number of factors. The risk factors for outbreaks after disasters are primarily associated with displacement of highly vulnerable populations. They are related to the proximity of safe drinking water and functioning latrines, the nutritional status of the displaced population, the level of immunity to vaccine-preventable diseases, and the access to healthcare services.29,43,52 Historically, large-scale, long-term displacement of populations as a result of flood disasters is uncommon. This likely contributes to the low overall risk for outbreaks.54 In high-income countries with adequate public health infrastructures, post-impact surveillance has only occasionally detected increases in life-threatening infectious diseases after disasters, and these increases have been relatively small.4,6,52 In comparison, in low-income nations, disaster recovery workers have reported larger outbreaks of endemic infectious diseases including cholera and typhoid, acute respiratory infections, and leptospirosis.39 Despite frequent public concern to the contrary, non-endemic diseases do not spontaneously emerge after flood disasters. Floods exacerbate diseases that are endemic to the affected populations.
Diarrheal Illness
Under flood conditions, there is potential for increased fecal-oral transmission of disease, especially in areas where the population does not have access to clean water and sanitation. Outbreaks of diarrhea occur in both high-income nations and low-income nations and are associated with locally endemic pathogens. The risk of diarrheal illness appears to be less for high-income countries, as compared to low-income countries. Diarrheal illness in high incomes countries most commonly manifests as a self-limiting gastroenteritis without a specifically identified pathogen. Flood-related outbreaks of life-threatening diarrheal diseases (such as paratyphoid and cholera) have been reported in very low-income nations.
Flood-Related Diarrheal Illness in High-Income Nations
In 1983, an outbreak of diarrheal illness was reported in Utah, possibly associated with contaminated water supply that resulted from flooding during the spring snow melt. Five routine bacteriologic samples from the source revealed coliform counts to be elevated above acceptable limits.35 A similar period of heavy water runoff associated with unseasonably warm weather and ash fall from the Mount Saint Helens volcano eruption in 1980 was also linked to an outbreak of diarrhea due to Giardia lamblia.53
After flooding caused by Tropical Storm Allison in Houston, Texas, in June 2001, fifty-four (12.9%) surveyed households reported at least one person with illness that occurred after the onset of flooding. Persons living in flooded homes were significantly more likely than those living in non-flooded homes to report illness; the only specific illness significantly associated with residing in a flooded home was diarrhea/stomach conditions.25 In 2002, in a village near Barcelona, Spain, an outbreak of shigellosis affected over 10% of the population. The outbreak was linked to consumption of drinking water that may have been contaminated after heavy rain caused floods.54 After Hurricane Katrina in 2006, clusters of diarrheal disease were reported in evacuation centers in four U.S. states; gastroenteritis was the most common acute disease complaint among evacuees in Memphis, Tennessee.39 Approximately 6,500 of an estimated 24,000 evacuees in Houston shelters visited Reliant Park medical clinic, and 1,169 (18%) persons reported symptoms of acute gastroenteritis. In stool samples from forty-four patients tested, norovirus was confirmed in twenty-two (50%) specimens; no other enteropathogen was identified.55
Two cases of toxigenic Vibrio cholerae O1 infection were reported in Louisiana after Hurricanes Katrina and Rita.56–58 However, there was no epidemic and was no evidence to suggest that there was an increased risk of cholera among residents of the Gulf Coast after these hurricanes.39
Flood-Related Diarrheal Illness in Low-Income Nations
Surveillance data showed an apparent mortality increase from diarrhea during the 1988 floods in Khartoum, Sudan,59 but a similar rise was also apparent in the same period of the preceding year.60 Routine surveillance data and hospital admission records showed diarrhea to be the most frequent cause of death following severe flooding in 1988 in Bangladesh, but again, the effect of the flood was not separately quantified from seasonal influences.49 Two devastating monsoon-related floods in Bangladesh in 2004 resulted in very large outbreaks of diarrheal disease reaching epidemic proportions throughout the capital city of Dhaka. Healthcare workers evaluated more than 17,000 patients in one hospital during one of these flood periods. Cholera was the most common cause of admission, and enterotoxigenic E. coli was also an important cause of acute watery diarrhea, particularly in children less than 2 years of age.39 In a large study undertaken in Indonesia in 1992 and 1993, flooding was identified as a significant risk factor for diarrheal illnesses caused by paratyphoid fever.43
Respiratory Infections
Whenever there is a lack of clean water among displaced populations, there is often a concomitant difficulty in maintaining adequate hygiene. This lack of hygiene can lead to not only diarrheal illness, but also acute respiratory infections. Reported incidence of acute respiratory infections increased fourfold in Nicaragua in the 30 days after Hurricane Mitch in 1998.43
Flooding may also result in episodes of near-drowning and pulmonary aspiration of floodwater. Direct inoculation of the pulmonary system with marine and soil debris may cause serious acute respiratory infections and systemic infections. Flood-related aspiration pneumonia is often polymicrobial.39
Vector-Borne Diseases
The relation between flooding and vector-borne disease is complex. The predicted impact of severe weather or floods on vector-borne illnesses is less certain than that of enteric infections. Severe weather can either increase or decrease the transmission of vector-borne illnesses.39,49 Such variance probably mirrors the complexity of a given situation, and partly reflects the prevalence of vector-borne diseases in the region before the disaster. Additional factors include: 1) the identity and ecology of the local vectors (some vectors prefer clean water, others prefer organically rich water; some prefer fresh water, others prefer water containing low amounts of salt); and 2) the impact of control programs or other interventions that minimize vector–human contact (for example, the use of larvacidal or insecticidal agents, access of survivors to nets or window screens, and access of survivors to shelters versus sleeping outdoors).39
Arthropod-Borne Diseases
Flood-Related Arthropod-Borne Disease in High-Income Nations
Floods are often followed by a proliferation of mosquitoes. In the United States, such disasters are rarely followed by outbreaks of arboviral disease, attributable mostly to the relatively low prevalence of vector-borne diseases in the region before the disaster.39,61
Heavy rains and flooding have been associated with outbreaks of St. Louis encephalitis in Florida, believed to be associated with the feeding activities of the responsible mosquito vector.39 In comparison, despite the proliferation of large populations of mosquitoes known to amplify transmission of arboviruses that cause St. Louis encephalitis and Western equine encephalitis after the Great Midwestern U.S. floods, surveillance data indicated minimal risk for arboviral disease above background levels in the disaster area. During the floods, forty-five counties (53% of the population) in Iowa reported vector problems. Mosquito vectors were found to exist in extremely high levels. Serum conversions were not detected in sentinel chicken flocks, nor were there any human cases of illness reported as resulting from mosquito vectors.26 As a consequence, contingency plans for large-scale mosquito adulticide were not implemented, resulting in an estimated cost saving of over $10 million USD. Despite the presumed low risk for mosquito-borne arboviral disease after flood-related disasters in high-income countries, surveillance programs are useful to assist with determining prevalence of large vector populations and preventing unnecessary expenditures associated with the application of insecticides implemented during prophylactic mosquito control.61
Flood-Related Arthropod-Borne Disease in Low-Income Nations
Malaria outbreaks in the wake of flooding have been reported in several very low-income nations with warm climates.43 Increased numbers of cases of drug-resistant malaria were noted after floods in Sudan62 and an outbreak of more than 75,000 cases of Plasmodium falciparum malaria occurred in Haiti after Hurricane Flora in 1963.63 A four- to fivefold increase in malaria incidence also occurred after a flood disaster in 2000 in Mozambique.61 However, after the 2004 Indian Ocean tsunami, no appreciable increase in the number of malaria cases was reported in Indonesia.63
Dengue transmission is influenced by meteorological conditions, however transmission has not been directly attributable to flooding. In Brazil, Indonesia, and Venezuela, rain, temperature, and relative humidity has been associated with patterns of dengue infection.39 Monsoon rains and floods have been associated with outbreaks of dengue fever in India. In Thailand, dengue was a common cause of fever in children after heavy rain-associated flooding.39
Rodent-Borne Diseases
Diseases transmitted by rodents may also increase during heavy rainfall and flooding because of altered contact patterns. Humans usually acquire leptospirosis after exposure to fresh water contaminated with the urine of infected animals, such as rats.
There have been reports of flood-associated outbreaks of leptospirosis from a wide range of countries including Argentina, Brazil, Cuba, India, Korea, Mexico, Nicaragua, Philippines, Portugal, Russia, Taiwan, and Hawaii and Puerto Rico in the United States.23,26,29,64 Investigations in France have documented a significant association between the emergence of leptospirosis and a combination of heavy rainfall and garbage collection strikes. In this case, trash left on the streets led to an increase in the surface rat population.65
Chemoprophylaxis with doxycycline is effective as a primary strategy for leptospirosis prevention among people who have high likelihood of occupational exposure or for those in areas of high endemicity. However, study results are inconclusive regarding the efficacy of doxycycline chemoprophylaxis in areas with high endemicity of leptospirosis in the setting of floods.66
Dermatological Conditions
Dermatological conditions, usually in the form of nonspecific rashes, are a commonly reported complaint during floods and other disasters.4,29 Among hurricane evacuees from the New Orleans area, a cluster of infections with methicillin-resistant Staphylococcus aureus (MRSA) was reported in approximately thirty pediatric and adult patients at an evacuee facility in Dallas, Texas. Three of the MRSA infections were confirmed by culture.58
Wound Infections
Wound infections are common after disasters. The destruction of the regional health infrastructure, the inability to wash wounds with clean water, and a shortage of topical or systemic antimicrobial agents can all lead to severe wound infections, even if the initial trauma was relatively minor. In 2005, after hurricane Katrina, twenty-four cases of Vibrio species bacterial wound infections were identified. Most patients had associated comorbidities that probably increased their risk of Vibrio wound infection, and many had been wading in floodwaters.39,58
There is no evidence indicating that the risk of tetanus is increased in flood-related lacerations; therefore standard immunization practices should be an employed, that is, a wound normally classified as “low-risk” remains so even if exposed to floodwaters.6 In comparison, the incidence of tetanus in the disaster setting has been associated with wounds that are highly contaminated with soil as result of high-energy traumatic inoculation occurring in low-income nations where patients are less likely to have had primary vaccinations and access to post-exposure tetanus prophylaxis. Clusters of tetanus cases were reported after the Indian Ocean tsunami as well as the Pakistan earthquake in 2005. However, these exposures were sustained during the initial trauma on the day of the event and not associated with exposure to floodwater or contaminated water sources. No subsequent cases were reported 2 weeks after the tsunami, indicating an association with the initial traumatic injury on the day of the event and not from wound exposure to floodwaters afterwards.63
Injuries
During a flood disaster, injuries are more likely to occur as people attempt to travel or evacuate through flooded areas and again when they return to dwellings to repair damage and clear debris. Hypothermia, with or without submersion injury, is seen in some flood casualties. Conductive heat loss due to immersion in any water less than 16–21°C may lead to hypothermia. Wet clothing and water immersion tend to conduct away core body heat even when the ambient air temperature is extremely warm, but less than body temperature. Convective heat losses increase in windy conditions.
Electrocutions have occurred as a result of downed power lines, electrical wiring, and improper handling of wet appliances. Injuries from fires and explosions from gas leaks also occur. Musculoskeletal and soft tissue injuries are frequent conditions associated with floods. Lacerations and punctures are common sequelae during post-flood cleanup and recovery activities.4,6
Although it is a recurrent public concern that animals such as snakes may be forced to seek refuge from rising floodwaters in areas that may be inhabited by humans, public health surveillance after floods has not indicated that wild animal bites have been a major issue.4,6 In contrast to wild animals, after Hurricane Floyd there were increases in reports of domesticated dog bites.50 Epidemiologists reported similar data from Iowa during the same year.26
In Missouri after the Great Midwest U.S. floods of 1993, injuries were reported through a routine surveillance system. During a 6-week period, a total of 524 flood-related conditions were reported, and of these 250 (48%) were injuries. These injuries were categorized as sprains/strains (34%), lacerations (24%), abrasions (11%) and other injuries (11%).8
Mental Health Effects
Multiple studies have reported severe social and health impacts in the setting of flood disasters.32,35,67–71 Social effects include disruption to people’s lives, relationships and communities, and the destruction of people’s homes.32 Long-term effects of flooding on psychological health may be even more significant than those for any other illness or injury.72,73 For many people, the emotional trauma continues long after the water has receded.
Factors that appear to make people more vulnerable to the development of psychological problems include:
Objective and subjective characteristics of the disaster – proximity of the victim to the disaster site; the duration of the disaster; the degree of physical injury; the witnessing of death or injury.72
Characteristics of the post-disaster response and recovery environment – community cohesion; secondary victimization; disruption of social support systems;47 lack of home-ownership and duration of displacement from home.35
Characteristics of the individual or group – history of psychological problems; elderly; unemployed; single parents; children separated from their families.72
In one study of the health effects of flooding in thirty locations in the United Kingdom, psychological effects were much more commonly reported after flooding than physical ones. Women also appeared to suffer markedly more frequently than men at the worst time of flooding.35 A number of psychological effects reported by flood victims have been strongly associated with reporting physical effects, particularly immediate effects.35
Increased morbidity and mortality following a flood may also result from heightened psychological stress.73 Psychiatric examinations of 224 children 2 years after the 1972 flood in Buffalo Creek, West Virginia, showed that 80% of the children were severely emotionally impaired by their experiences during the flood.74 Five years after the flood caused by Tropical Storm Agnes in Pennsylvania, perceived health problems were reported more commonly by flood-affected respondents than non-affected controls.74
Anxiety and Depression
There is considerable evidence for the development of anxiety and depression among flood-affected populations. Most studies are from high- or middle-income countries, including Australia, Poland, the United Kingdom, and the United States, but there is also a study from Bangladesh.47 A few studies have examined flood-related mental health impacts on children. One 1993 study found post-flood changes in behavior among children 2–9 years old.47
Post-Traumatic Stress Disorder
Studies in Europe and North America have revealed post-flood psychiatric disorders among flood-affected populations that meet the criteria for post-traumatic stress disorder (PTSD).32,47,68,71 One longitudinal study found 15–20% of people affected by a disaster had symptoms of PTSD.73 Other studies after the 1997 floods in Poland suggested long-term negative effects on the well-being of children aged 11–14 and 11–20 years with increases in PTSD, depression, and dissatisfaction with life. Six months after Hurricane Floyd in the United States, similar findings were described for disaster-affected children aged 9–12 compared with controls.47
Studies of flood survivors in India found significantly higher scores for PTSD and depression among people more than 60 years old compared to all other groups.75 Studies by Huang and colleagues found that a simple risk score model could be used to predict adult PTSD victims after floods in China.76
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