The Zermatt typhoid outbreak in 1963

Abstract

1. A description is given of the outbreak of typhoid fever in Zermatt in 1963.2. There were 437 cases and three deaths, a case fatality rate of 0·7%.3. Information from 260 tourists established that the initiation of infection was explosive and allowed the period of infection to be determined.4. The mean incubation period of various tourist fractions was probably between 16 and 18 days but was found to be significantly longer (20–21 days) for hotel employees.5. The evidence favours a waterborne outbreak. Studies of the water supply showed that the catchment area and the surface streams and their water were liable to contamination.6. One particular stream, the Zmuttbach, constituted a greater danger than the remainder.7. The water purification at the treatment station was inadequate; in particular the holding time for chlorination was too short, and the required concentration of 0·2 p.p.m. was not reached consistently. In addition, there were periods during which completely unchlorinated water reached the general supply.8. It was discovered, some months after the epidemic, that there was leakage of sewage, probably of long standing, into the chlorination tank. This seems to be the most likely source of the water contamination.9. The typhoid excretor responsible for the outbreak was not discovered.