Young children, the elderly and others with compromised immune systems should be especially careful. The disease does not spread easily. It cannot be passed from person to person, only from infected birds to Culex mosquitoes and from mosquitoes to humans. Even if a person is bitten by an infected mosquito, only a small proportion of persons infected develop severe disease. Since the first instances of disease were reported, public health officials in New York City have identified 11 cases of St. Louis encephalitis and three deaths due to the disease.
Infection often leads to bloody diarrhea and occasionally to kidney failure.
Most illness has been associated with eating undercooked, contaminated ground beef. Infection also can occur after drinking raw milk and after swimming in, or drinking water contaminated with sewage or animal waste. H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness. The combination of letters and numbers in the name of the bacterium refers to the specific markers found on its surface and distinguishes itself from other types of E. coli.