West Nile virus activity in the Washington region has been minimal this year, with no human cases reported in the District, Maryland or Virginia, despite an early outbreak in the western United States that has left about 100 people stricken.

This week, District officials reported their first mosquitoes of the year to test positive for West Nile this year. Virginia has identified 13 positive mosquito pools, plus three horses, two crows and one blue jay that have succumbed. Maryland has reported no activity this year.

By contrast, Arizona has reported 66 people infected with the virus, the most in the nation, according to the latest figures on the federal Centers for Disease Control and Prevention's Web site. Officials attribute the relative dearth of local West Nile activity to the fact that the virus has been in the eastern part of the country longer and the public is more aware of the risks than in the western United States.

"I'm sure the people out there did not expect West Nile to hit as hard as it did," said Suzanne Jenkins, an assistant state epidemiologist in Virginia. "I'll bet there's a lot more mosquito repellent used in Virginia than there was three or four years ago."

West Nile symptoms range from mild, flulike discomfort to encephalitis and meningitis. Experts also say that the majority of West Nile patients do not become severely sick and that the population at risk for infection is small, mainly the elderly. Many people in the region who contract the virus are unaware of it, and typically only the most severe West Nile cases, involving people who have contracted meningitis or encephalitis, are reported.

Regional health officials warn that it is too soon to tell whether the relatively light West Nile activity will continue, or whether the region will face a more serious outbreak.

"I think it's too early to tell," Jenkins said. "Every year at this time, I keep my fingers crossed and hope we don't have a problem like some of the other states have had."

Cyrus R. Lesser, chief of the Maryland Department of Agriculture's mosquito control section, said, "We're hoping cautiously -- very, very cautiously optimistic -- that we're going to see a drop in the activity this year."

The number of people who died of West Nile virus in the region dropped last year, despite concerns that a large mosquito population spawned by wet conditions would spark a larger outbreak than the previous year.

In 2003, Maryland had eight West Nile-related deaths, while one person in Virginia succumbed, and no one in the District. In 2002, West Nile virus claimed 11 lives in the region: seven in Maryland, and two each in Virginia and the District.

Last year, Maryland also disclosed an increase in the number of people who contracted West Nile, with 73 cases, compared with 36 in 2002. Virginia reported 26 human cases in 2003, down from 29 cases the year before. The District reported three human cases last year, compared with 34 in 2002.

The virus, first detected in the United States in 1999, continued to spread across the country last year. The number of human cases more than doubled nationwide, to 9,862, from 4,156 in 2002. Colorado led the nation with 2,947 cases and 63 deaths, according to the CDC Web site. However, the number of fatalities was down, from 284 deaths nationwide in 2002 to 264 last year.

In 2002, West Nile spread from population centers in the Baltimore and Washington suburbs to Maryland's Eastern Shore and other rural areas, and that trend continued last year in Maryland and Virginia.

Local health experts credited the region's relatively low toll last year to a well-coordinated response from local agencies and a high level of public awareness. That success came despite an increase in the number of mosquito pools carrying West Nile virus in Maryland and Virginia.

This year, by contrast, despite normal breeding conditions, "all of our mosquito populations have been very much below normal," Lesser said.

Experts have "no good explanation" as to why the mosquito population is down, except for speculation that "the tidal flooding from Hurricane Isabel . . . might have washed out a lot of mosquito breeding areas" last year, Lesser said.

Officials plan to continue the public education campaign that was initiated locally after the outbreak of the disease. Officials ask residents to continue to take the traditional precautions: Wear insect repellant when outside, and remove standing water from around homes.