The 1991 cholera epidemic in Peru : not a case of precaution gone awry

Tickner, J. and Gouveia-Vigeant, T. (2005) Risk Analysis, 25 (3); 495-502.

In late January 1991, patients presenting at northern Peruvian coastal hospitals had Vibrio cholerae identified, marking the start of an outbreak that affected over 300,000 people by the end of the year. The epidemic spread rapidly to neighbouring Brazil , Colombia , Ecuador and up the coast to Guatemala , Panama and Mexico with more than 1.3 million cases of cholera occurring in the years 1991-1995. Consumption of seafood was originally suspected as the vehicle of transmission however contaminated drinking water was an important factor in the rapid spread of the disease. This epidemic is often cited as an example of how the precautionary principle can result in risk tradeoffs leading to adverse health effects. The precautionary principle calls on decision makers to take preventive action when there is evidence to indicate that there may be a potential for harm to public health and the environment, even though the nature and the magnitude of the harm are not fully understood scientifically. It has been argued that the Peruvian government stopped chlorinating drinking water supplies in the country following the publication of reports on the health risks of disinfection byproducts (DBPs) because of concern about this new hazard. This paper examines whether the decision to stop chlorinating was because of the concern over DBPs, whether the decision resulted in the 1991 Peruvian cholera epidemic and was this a failure of the precautionary principle.

To answer these questions, investigations of the epidemic in the cities of Iquitos and Trujillo were analysed, the literature was reviewed and interviews were conducted with leading Peruvian infectious disease researchers. It seems that concerns were raised by some Peruvian health and water treatment authorities about DBPs however the evidence indicates that there was no decision to stop chlorinating drinking water. Any reluctance to expand chlorination was most likely due to economic and infrastructure limitations instead.

There were many different causes of the cholera epidemic including the lack of proper disposal of human waste, limited and poorly maintained water treatment and distribution systems, poor hygiene practices which resulted in contamination of food and water, dumping of cholera-contaminated sewage in coastal waters and global climate changes which may also have contributed. Many of these factors were not recent events and had existed for years. It is thought that perhaps the most important root cause of the epidemic was the poverty and social and economic inequities and marginalisation that inhibited access to clean drinking water. In Peru in the 1980s there was a major migration to the capital city Lima and coastal cities as a result of rural poverty and civil strife. At the same time there were low levels of investment in water treatment and sanitation. Many of the cities could not cope with the influx of population and did not have the basic water infrastructure to deal with it.

The 1991 cholera epidemic is not a case of failure of the precautionary principle but rather an inadequate public health infrastructure that could not deal with this microbial water contamination. The case cities of Iquitos and Trujillo show that even if chlorination and other treatment methods had been widely used, other problems with the distribution systems would have still allowed the water to become contaminated. When using decision tools, precaution is needed and some failure is expected, however in this case failure of the precautionary principle is not demonstrated.

Comment This paper refutes other reports on the South American cholera outbreak which claim that decisions to cease chlorination were made on the basis of fears over adverse health effects of DBPs. (See Health Stream Issue 38, page 6).