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Current Trends Flood Disasters and Immunization -- California

The heavy rains and floods in many areas of California this year have disrupted some community water supplies and sewerage systems. Such natural disasters often result in public concern about possible contagion from flood waters due to contamination by sewage or animal carcasses.

Studies of flood and earthquake disasters have shown that communicable disease outbreaks rarely result from such events (1). Nevertheless, there is often a public demand for emergency mass immunization, especially against typhoid fever, despite the fact that epidemic typhoid has been conspicuously absent following natural disasters in the United States (where typhoid incidence is low) and in developing countries (where typhoid is endemic). Additionally, it takes several weeks for typhoid antibodies to develop, and even then, immunization provides only moderate protection against the disease. Also, adverse vaccine reactions are common (fever, headache, malaise, swelling and pain at the injection site) and burden flood victims and relief workers with more stress. Mass tetanus immunization programs are also not indicated, as floods pose no additional risk of tetanus. Management of flood-associated wounds should include appropriate evaluation of tetanus immunity (and immunization if indicated) as at any other time.

Of greatest importance in preventing enteric disease transmission when water and sewerage systems have been compromised is to assure that water and food supplies are safe to consume. When water contamination has occurred or is suspected (e.g., drop in water pressure, discoloration, turbidity, or unusual odors) only water bottled or trucked from a safe source, water brought to a vigorous boil, or water appropriately disinfected* should be consumed until health authorities indicate that public supplies are again safe to drink. Questions about the safety of foods exposed to flood waters or potentially spoiled due to interrupted refrigeration can be directed to local public health sanitarians.

Flood victims and relief workers should always wash their hands with soap and water (boiled or disinfected when no regular safe supply is available) before preparing or eating food, after toilet use, and after participating in flood cleanup or handling potentially contaminated articles.

While communicable disease outbreaks in the United States are rare after flooding, some potential does exist for waterborne disease transmission (e.g., enterotoxigenic Escherichia coli, Shigella, Salmonella, hepatitis A, Norwalk virus agents, and even such infections as leptospirosis and tularemia); therefore, flood-affected communities should be under close surveillance.

Mass immunization programs at the time of natural disasters are counterproductive and divert limited manpower and resources from other relief tasks. Such immunization programs may also give the public a false sense of security, leading to neglect of the basic rules of hygiene and sanitation that are far more important than immunizations in preventing infectious diseases that flood waters may spread. Reported in California Morbidity, March 11, 1983 (9).


  1. Western KA. Epidemiologic surveillance after natural disaster. Washington, DC: PAHO/WHO, 1982 (Scientific publication no. 420).

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