Waterborne epidemics in Finland in 1998-1999

Fourteen waterborne epidemics occurred in Finland during 1998-1999. About 7 ,300 illness cases were registered in these outbreaks. All except one of th e waterborne epidemics were associated with undisinfected groundwaters. An equal number of waterborne epidemics occurred in public and private water s ystems, but most cases of illness occurred in public water systems. The thr ee largest epidemics comprised 6,700 illness cases. Insufficient purificati on treatment unable to remove Norwalk-like viruses caused the only waterbor ne epidemic in a surface water plant. The main reasons for groundwater outb reaks were floods and surface runoffs which contaminated water. Norwalk-lik e viruses caused eight and Campylobacter three of the outbreaks. In two cas es the epidemic ceased by the exhaustion of susceptible persons in the expo sed community but in most cases it was terminated by changing the water sou rce, boiling the drinking water, and starting chlorination.