A San Francisco man has been diagnosed with West Nile virus -- the first locally acquired human case reported in the city since 2005, health officials said.
The patient, who is recovering at home, had not recently traveled outside the Bay Area, suggesting that he contracted the virus somewhere in the region, according to the San Francisco Department of Public Health.
There is no way to determine whether the virus was contracted in San Francisco or in one of the surrounding counties, health officials said.
Another San Francisco resident was diagnosed with West Nile virus in 2010, but it is believed that person was infected through an organ transplant, health officials said.
Earlier this month, a dead bird infected with West Nile was found near City College of San Francisco.
Health department officials said the find indicated that the virus was present in the city at the start of San Francisco's warmer season, when mosquitoes tend to breed in stagnant water.
In response to the human case, the city this week issued a health update to medical providers requesting that clinicians watch for symptoms of the disease and report any suspected cases to the health department.
Local agencies are urging residents to eliminate standing water from storm drains, water basins, ornamental ponds, lawns, bird baths, wading pools and leaking pipes to limit mosquito breeding.
Mosquito bites -- the means by which the disease is spread to humans -- can be avoided by wearing long pants and shirts, using repellants on exposed skin and placing screens on windows, public health officials said.
People over age 50 and those with weakened immune systems are particularly vulnerable to the virus. Anyone who has a fever and headache for more than seven days may have the virus and is advised to seek treatment.
Residents who discover significant mosquito activity should report it to public health officials by calling 311. Those who find a dead bird are
urged to notify the state of California by calling (877) WNV-BIRD.