September 30, 2005
Eileen Shields, Public Information Officer, 415/554-2507
San Francisco Announces Second West Nile Virus Case
Patient Contracted Virus Outside of San Francisco
San Francisco, CA—San Francisco health officials have confirmed the
City’s second case of West Nile Virus (WNV). The patient, a middle aged
woman, is convalescing in a nursing care facility.
Details of the woman’s travel history and the WNV incubation period lead
disease control investigators to conclude that the woman contracted the
disease in the Sacramento area and not in San Francisco. City officials
expect cases in San Francisco residents who travel to where West Nile
Virus transmission is active.
“City residents need to stay vigilant about protecting themselves and
their neighbors from mosquito bites by preventing mosquito breeding,”
observed Rajiv Bhatia, MD, Director of Environmental Health. “The
elderly, the very young and anyone with a chronic illness need to be
especially careful by taking personal precautions. This is a preventable
disease that can have critical outcomes in vulnerable populations.”
Over 40 San Francisco birds have been tested for the virus this year and
none have been found positive. Typically, WNV cases in birds precede
So far in 2005, 753 human cases of the West Nile virus have been
reported in 38 California counties, with most of the cases in Sacramento
and Riverside Counties. There have been 16 fatalities. In the United
States, almost 10,000 human cases of WNV have been reported since it was
first detected in the United States in New York in 1999.
Most individuals who become infected with WNV will not experience any
illness. Others will have only mild symptoms, such as fever, fatigue,
nausea, headache, muscle aches, skin rash, or swollen lymph nodes.
However, WNV can affect the elderly and individuals with compromised
immune systems with more severe illness.
WNV is transmitted to humans and animals through a mosquito bite.
Mosquitoes become infected when they feed on infected birds.
Human-to-human transmission of WNV does not occur.
San Francisco is taking several steps to limit risks to residents. The
City’s mosquito control program includes: collecting birds for testing,
monitoring ponds and other possible mosquito breeding sites, trapping to
detect high numbers of mosquitoes, treating sewer catch basins to
prevent breeding, and educating residents and owners about removing
standing water from private property and avoiding mosquito bites.
Individuals can reduce their risk of mosquito-borne diseases by taking
- Avoid spending time outside when mosquitoes are most active,
especially at dawn and dusk.
- When outdoors, wear long pants and long-sleeved shirts.
- Apply insect repellent according to label instructions.
- Make sure that doors and windows have tight fitting screens. Repair or
replace screens that have tears or holes.
- Eliminate all sources of standing water on your property that can
support mosquito breeding.
Contact the Department of Public Health, Mosquito Control program at
415-252-3806 if there is a significant mosquito problem where you live
More information about West Nile Virus and San Francisco’s prevention
activities can be found at the websites,