Leptospirosis: what all triathletes should know when open-water swimming

With the peak of the competitive season looming, Andrew Hamilton takes a look at research suggesting that triathletes should exercise caution when swimming in open water…

Although it’s the most natural form of swimming known to man, open water swimming presents triathletes with a number of challenges and potential hazards. These include coping with waves, being able to navigate efficiently and coping with cold water temperatures – none of which is an issue in the pool! Then of course there are the psychological challenges; pondering the tens or even hundreds of feet of inky black water below them while you swim can spook even accomplished triathletes. Add to that the issue of foreign objects such as fish, jellyfish and seaweed; on those inevitable occasions when you discover you’re not alone in the water, you need to hold your nerve and keep your imagination in check!

Ironically however, none of these issues are likely to present a real problem to well-prepared triathletes who train and/or compete in open water, particularly in a race situation, where marshals, safety boats and first aid facilities are on hand. By contrast, recent research suggests that a much more potent form of danger in the water facing triathletes is one that you’re probably unaware of – indeed, have probably never heard of – leptpspirosis (see panel below).

What is leptospirosis?

Leptospirosis is a bacterial infection caused by a strain of bacteria called leptospira, which is spread by animals. Clinical manifestations of leptospirosis begin a few days after the initial exposure and range from mild flu-like symptoms such as headaches, chills and muscle pains to life-threatening disease characterised by jaundice, organ failure and internal bleeding.

Although more prevalent in the tropics and sub-tropics (where it has more recently been categorised as a re-emerging infectious disease(1)), leptospirosis in Europe has been historically associated with agricultural occupations. This is because the disease can be spread to humans from animals that carry leptospira bacteria via contact with soil or water contaminated with the animal’s urine. However, recent evidence is emerging that leptospirosis is becoming an increasing threat to those who use stretches of open water for recreational purposes in more northerly latitudes.

Leptospirosis and triathletes

One of the earliest scientifically documented outbreaks of leptospirosis among triathletes came after the Springfield Triathlon in Illinois, 1998(2). Following a number of reports of illness among participants, scientists investigated by conducting clinical tests on the triathletes who had fallen ill and by taking lake water samples to determine whether leptospiral contamination was a factor. In total, 98 (12%) of the triathletes reported being ill and blood tests subsequently showed that most of these cases were explained by leptospirosis. Forty percent of the laboratory-confirmed cases were hospitalised. Water testing also showed that the heavy rains that preceded the triathlon were likely to have increased leptospiral contamination of Lake Springfield (heavy rain can wash leptospiral bacteria from the soil into rivers, lakes and the sea). This was borne out by the fact that among the triathletes, ingestion of one or more swallows of lake water was a predominant risk factor for illness.

Unsurprisingly perhaps, an isolated outbreak of leptosporosis attracted little attention from researchers. However, as more and more outbreaks have been documented, scientists have begun to sit up and take notice. For example, a study on canoeists after a 2001 white water event on the River Liffey (also the swim venue for the Dublin Triathlon) showed that just over 9% of the participants had contracted leptospirosis as a result.

Symptoms typically included fever, chills, red eyes and shortness of breath and five cases were severe enough to require hospitalisation. As in the Springfield Triathlon, swallowing more than one mouthful of water was associated with an increased risk of developing the disease and heavy rainfall prior to the event was believed to have contributed to this outbreak.

Following the 2006 Heidelberg Triathlon in Germany, another outbreak of leptosporosis was confirmed(4). Although there were only five laboratory-confirmed cases among the 507 participants, the researchers noted that it was the first outbreak of leptospirosis related to a competitive sports event in Germany. As in previous studies, the heavy rain, which preceded the event (see figure 1) was thought to be a major issue. The researchers also noted that open wounds rather than water swallowing was the key risk factor – possibly because the levels of water contamination were lower and the swim shorter than in Springfield.

Figure 1: Rainfall and temperature around the time of the 2006 Heidelberg Triathlon

Rainfall and temperature records for Heidelberg around the time of the triathlon (6th August, 2006) – the date of the triathlon is indicated by the red arrow.

One of the most recent cases of leptospirosis in triathletes occurred in Austria after the Langau Triathlon in July 2010. Once again, heavy rains preceded the event and once again, some triathletes were subsequently admitted to hospital, including one competitor with kidney failure who required haemodialysis for three weeks. As in previous studies, the researchers were keen to emphasise that users of bodies of freshwater must be aware of an existing risk of contracting leptospirosis, particularly after heavy rains. They also suggested that triathletes face an especially high risk because of the suppression of the immune system that naturally occurs after heavy, strenuous exercise such as a triathlon.


Leptospirosis is a potentially serious condition and triathletes (and open-water swimmers) need to be aware of the possible risks, especially when participating in open water training/triathlon swims after a period of heavy rainfall. Having said this, it’s worth adding that each year hundreds of thousands of triathletes train and compete in open water with absolutely no ill-effects, and the risk averaged out over all events and competitors is very small indeed. Therefore, while it pays to mindful of the risks – especially following heavy rain – you shouldn’t be deterred from the freedom and enjoyment that open water swimming can provide!

Practical recommendations

  • Be aware that open-water swimming after heavy rainfall carries an increased risk of contracting leptospirosis and avoid if possible.
  • During longer swims, minimising the amount of water swallowed can reduce your risk of infection.
  • Always keep any open wounds covered with a waterproof dressing. The use of a triathlon suit can also reduce the risk of contracting leptospirosis via skin transmission.
  • Any mild flu-like symptoms occurring in the days following a session of open-water swimming should be taken seriously; get checked out by your GP immediately as delay in treating leptospirosis can result in very serious complications.
  • Triathlon race organisers should conduct regular water quality monitoring testing for leptospiral bacteria at open water swim venues to ensure risks to competitors are minimised.


  1. Clin Microbiol Rev 2001, 14:296-326.
  2. Clin Infect Dis. 2002 Jun 15;34(12):1593-9
  3. Epidemiol Infect. 2004 Apr;132(2):195-200
  4. BMC Infect Dis. 2010 Apr 10;10:91
  5. Wien Klin Wochenschr. 2011 Dec;123(23-24):751-5

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