Chapter 19. Microbiology and infection
Routes of infection
Infection can be spread by a number of different routes, these include:
• Droplet spread – the common route of infection for respiratory disease
• Direct contact – hand to wound, mouth to mouth, biting, injection
• Faecal–oral – transmission on the hands from the lower GI tract to the mouth
• Indirect contact – contaminated material or equipment is brought into contact with another casualty.
Terminology
Bacteria
Small, unicellular organisms that have evolved to live in very specialised environments.
Viruses
Much smaller organisms that cannot be seen with a normal light microscope.
Carrier
Someone harbouring a microorganism but not showing evidence of disease.
Source
Area in which a microorganism grows.
Reservoir
The vehicle of transport of infection (e.g. the hands in a faecal–oral transmitted infection).
Incubation period
The time during which the microorganism is multiplying in body tissue before the signs and symptoms of illness have developed.
Infectious period
The time during which the infection may be transmitted to other people.
Important infectious diseases in the UK
Bacterial Infections
Tuberculosis
Organism
• Bacteria of the mycobacterium species.
Symptoms and signs
• Shortness of breath
• Cough
• Discharging skin sinuses in lymph node involvement (rare).
Mode of spread
• Droplet
• Direct spread.
Incubation period
• 4–8 weeks.
Infectious period
• Until treated.
Prehospital precautions
If a patient with active tuberculosis has been transported, the ambulance must be thoroughly aired, linen laundered and contaminated respiratory equipment such as face masks and tubing destroyed. Concerns about staff contracting the disease should be discussed with occupational health.
Notes
The incidence has recently risen in the UK, possibly owing to the increasing number of immigrants, a decrease in the uptake of vaccination and poor living standards in inner cities.
Patients continue to be infectious until their illness has been treated. All paramedic staff should ensure that they are fully immunised against tuberculosis and have a Heaf test (intradermal tuberculin) every 3 years to check their immunity.
Meningitis
Meningitis is an infection of the membranes that surround the brain. When the infection is bacterial and organisms spread to the blood stream, septicaemia is present.
Organism
Bacteria or viruses. The most common bacteria are Haemophilus influenzae, Neisseria meningitidis and Streptococcus pneumoniae.
Symptoms and signs
• Headache
• Photophobia (light hurting the eyes)
• Neck stiffness
• Non-specific flu-like illness
• Bruising rash (non blanching) in associated septicaemia – especially N. meningitidis.
Mode of spread
Droplet.
Incubation period
Incubates for 2–3 days in meningococcal meningitis (due to the bacteria N. meningitides).
Infectious period
Infectious until treated.
Prehospital precautions
When transporting such a patient, a face mask should be worn and the ambulance and all equipment thoroughly cleaned afterwards. Hand washing is essential. If the final diagnosis is proved to be meningococcal meningitis, the occupational health department will consider giving a course of antibiotics to reduce any possible risk of acquiring the infection, although prophylactic antibiotics are not usually given to paramedic or medical staff unless they have been ‘kissing’ contacts (mouth-to-mouth ventilation).
Notes
The child with meningococcal disease may deteriorate very rapidly and must be administered benzyl penicillin and transported to hospital as soon as possible.
Whooping cough
Organism
Bordetella pertussis (bacterium).
Symptoms and signs
• Severe cough, with characteristic inspiratory whooping sound between bouts
• Vomiting
• Weight loss
• Pneumonia.
Mode of spread
Droplet.
Incubation period
Incubates for 7–10 days.
Infectious period
From 7 days after exposure until 21 days after first symptoms.
Prehospital precautions
Whooping cough does not represent a great risk to paramedic staff, but an ambulance should be thoroughly cleaned and aired if a child with the illness has been transported.
Notes
Whooping cough mainly affects children and is most severe in those under 6 months of age. The disease often lasts several months.
Viral infections
Hepatitis A – infectious hepatitis
Organism
Hepatitis A virus.
Symptoms and signs
• General malaise
• Jaundice
• Nausea and vomiting.
Mode of spread
Faecal–oral.
Incubation period
Incubates for 15–40 days.
Prehospital precautions
Universal precautions. Care when handling sharps. Report personal contamination immediately.
Notes
Common in conditions of poor sanitation and tends to occur in outbreaks, for instance in prisons or mental health institutions. The disease tends to run a benign course and usually resolves over a period of 1–2 months.
Hepatitis B – serum hepatitis
Organism
Hepatitis B virus.
Symptoms and signs
• General malaise
• Jaundice
• Nausea and vomiting
• Liver failure.
Mode of spread
• Intravenous (including dirty needles)
• Sexual contact.
Incubation period
Incubates for 40–160 days.
Infectious period
Variable – beware chronic carriers.
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