ACTIVE SURVEILLANCE FOR VIBRIO-CHOLERAE-01 AND VIBRIOPHAGES IN SEWAGEWATER AS A POTENTIAL TOOL TO PREDICT CHOLERA OUTBREAKS

The 1991 Peruvian cholera epidemic has thus far been responsible for 6 00,000 cholera cases in Peru. In an attempt to design a cholera survei llance program in the capital city of Lima, weekly sewage samples were collected between August 1993 and May 1996 and examined for the prese nce of Vibrio cholerae O1 bacteria and V. cholerae O1 bacteriophages ( i.e., vibriophages). During the 144 weeks of surveillance, 6,323 cases of clinically defined cholera were recorded in Lima. We arbitrarily d efined an outbreak as five or more reported cases of cholera in a week . The odds of having an outbreak were 7.6 times greater when V. choler ae O1 was present in sewage water during the four previous weeks compa red with when it was not (P < 0.001). Furthermore, the odds of having an outbreak increased as the number of V. cholerae O1 isolations durin g the previous 4 weeks increased (P < 0.001). The adds of having an ou tbreak were 2.4 times greater when vibriophages were present in sewage water during the four previous weeks compared with when they mere not , but this increase was not statistically significant (P = 0.15). The odds of having an outbreak increased as the number of vibriophage isol ations during the previous 4 weeks increased (P < 0.05). The signaling of a potential cholera outbreak 1 month in advance mag be a valuable tool for the implementation of preventive measures, In Peru, active su rveillance for V. cholerae O1 and possibly vibriophages in sewage wate r appears to be a feasible and effective means of predicting an outbre ak of cholera.