The public health watchdog Valvira is warning swimmers who’ve come down with a so-far unidentified stomach bug after a dip in the lake to stay out of the water for at least two weeks after their symptoms subside.
“Those who’ve fallen ill should remember that although they feel better, their stools may still contain norovirus. They should avoid going to beaches for a couple of weeks because there is no chlorine to destroy the virus. They may inadvertently contaminate others and spread the infection,” said Valvira chief inspector Jaana Kilponen in an Yle interview.
Nearly 1,000 swimmers in Oulu, Tampere and Sipoo have experienced symptoms consistent with a stomach infection after apparently swimming in lake water. Water samples tested in Oulu have revealed the presence of norovirus and adenovirus, which cause gastroenteritis and respiratory as well as gastrointestinal illnesses respectively. Now 71 swimmers in Oulu's Lämsänjärvi have fallen ill.
The symptoms reported in different parts of the country are all consistent with a norovirus infection, and include violent vomiting, diarrhoea and in some cases a high fever.
“So far the victims have been young children and youths who may have ingested water orally while playing (in the water). With bad luck, just one gulp would be enough,” Kilponen explained.
Samples may not tell all
Authorities are now extracting water samples from beaches where large numbers of swimmers have fallen ill. However according to Kilponen it may be difficult to identify the factors causing the symptoms in natural water sources.
“Whether or not we find anything may be a matter of chance. However with such a high number of patients we may be able to isolate something from their stool. Of course making the link between cause and effect would require finding the same populations in human and environmental samples,” she added.
The Valvira inspector said that it’s difficult to assess when lake waters will once more be free of pathogens. She did point out however, that flowing water dilutes viruses, while UV radiation destroys them.
Patient follow-up important
Tampere city epidemiologist Sirpa Räsänen has advised locals to seek medical attention if their children’s symptoms are so extreme that they have little energy for anything else but sleep.
“The younger the child the more we have to be prepared to get a medical evaluation. The duration of the symptoms isn’t the main factor, but rather how the child feels and whether or not they are being well hydrated at home,” Räsänen told Yle.
She added that the most critical aspect of care involves administering copious amounts of fluids.
“The vomiting or diarrhea will not necessarily subside but the illness will run its course. The comfort of a child or adult can be influenced by the amount of fluid that they can keep down,” she concluded.
