Scientists in Canada looked at 1,252 people who were infected with giardiasis during an outbreak in 2004, and when the researchers interviewed the people three years later, they found that 39 per cent suffered from Irritable Bowel Syndrome (IBS) and 30 per cent suffered from chronic fatigue. In 2010, the incidence of IBS in the group had decreased from 39 per cent to 32 per cent, and those still reporting chronic fatigue problems fell to 15 per cent. The scientists concluded that not only was exposure to the parasite a ‘significant risk factor’ for persistent IBS and fatigue, but it was also worse for older people, with age increasing the risk of ongoing chronic fatigue.
Other investigations into the longer term effects of travellers’ illnesses have shown similar results. For example, a study published in 2013 that collected data on over 42,000 people who had been treated for illness following overseas travel found that more than 40 per cent of travellers who reported gastrointestinal symptoms lasting more than two weeks suffered from chronic fatigue or IBS. The same study showed that giardia was the most common cause of gastrointestinal illnesses; and that most cases of giardiasis occurred in South and Central Asia countries, particularly India.