PRECAUTIONS AGAINST INFECTION
E.coli or cryptosporidium), or from some chemicals, and while these would not in themselves normally be life-threatening, they can mask the later symptoms of leptospirosis.
The incubation time depends on the strain of bacteria involved, as some strains reproduce faster in human blood than others, but the main factor is the size of the ‘inoculum’ – the dose of bacteria that entered the patient during their exposure. Although it’s perfectly possible to be infected from a single bacterium, in reality the illness develops because the rate that the bacteria are reproducing is faster than the patient’s immune system can control. Bacteria grow by splitting in half, so one becomes two, two become four, and so on. If the patient received a large number of bacteria from the initial contact then the numbers in their bloodstream will be larger, and increase faster – hence the illness develops sooner.
It’s very difficult to predict the incubation time in a patient, but in very general terms the concentration of bacteria in the inoculum will be important (water from a large clean river will have many times less bacteria per litre than urine direct from a rat) and the volume that enters the body (infection via small cuts to the skin usually involve very small volumes of liquid, but swallowing water after a fall into a lake will of course involve far more. The balance of course is that the situations where patients suffer a high-volume intake are usually those where the liquid has a low concentration (you are unlikely to fall into a tank of rat urine).
To minimise the chances of infection, the only truly effective way is to avoid contact with contaminated water and animals, thus avoiding exposure to the bacterium. If you are in a high risk area, you should always attempt to minimise contact, as there are many hundreds of other organisms that can lurk in the water apart from Leptospira. Unless you are required to enter the water, you should stay away from it. Animals themselves present a risk while infected, as their body fluids can contain the bacteria.
WATER
The vast majority of human cases are from contaminated water, and of those the majority are occupational cases from areas of the world where agriculture and rodents mix – rice-farming, cane-growing and so forth. Recreational exposure is next, with cases amongst swimmers being the obvious top grouping. Lowest of the risk groups is occupational exposure in the developed world – water and sewer engineers, construction, pest control and so on.
Clearly there are problems in preventing exposure in the highest risk activities (rice- farming and such) and in those areas the only option is to be aware of symptoms and seek early treatment. At this time there is no universally agreed human vaccine, and the preventative use of antibiotics can only be considered for short periods.
Swimming is the greatest risk and several cases are reported each year from swimming in contaminated water (both in the developed world and in activities such as adventure racing). There is no practical way to prevent exposure as some water will always enter the mouth. For one-off activities such as expeditions there is an argument
for using a preventative antibiotic (doxycycline), which can offer increased resistance to illness for a few weeks. It should never be used long-term.
Anglers and bankside/sewer workers should wear splashproof clothing and especially gloves. Anglers are at higher risk as it is reasonably common to cause minor cuts with hooks, knives and the like, and this greatly increases the ease by which the bacteria can enter the body. Fish caught from suspect areas should of course never be eaten. Whilst cooking does in theory kill any bacteria within a fish, very often the level of cooking is insufficient to guarantee safety.
Recreational exposure (swimming, skiing, sailing, caving, etc) is clearly done at the person’s own risk and they must weigh up their own balance of risk vs. desire. The same preventative measures apply – minimise the risk of water entering the body by any and all means. Consider antibiotics if the risks are very high, and be aware of the symptoms and seek treatment immediately. There are no ‘quick fixes’ to prevent infection. Some swimmers wash their mouths with antibacterial rinse, though this has not been proved to offer any significant benefit other than keeping their teeth clean.
Scuba divers, who are particularly at risk, should opt for drysuits and try as much as possible to avoid swallowing any water when purging or changing regs. Commercial divers are required by their employment regulations and insurance to comply with strict rules when working in contaminated water, these include the use of hard-hat systems, wash-down stations and regular medical testing.
Remember that this advice applies only to those working in FRESH water environments. The risks in salt water are virtually zero.
The Report • June 2017 • Issue 80 | 67
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