The West Nile virus has killed a fifth Louisiana resident and infected 14 more people in what health officials said Tuesday is the nation's biggest outbreak since the disease was first detected in the United States in 1999.

Seventy-one Louisiana residents have been confirmed to have the mosquito-borne disease. Before now, the largest outbreak had been the first, when 62 people became ill and seven of them died in New York three years ago.

The latest to die was a 76-year-old woman from St. Tammany Parish, on the north shore of Lake Pontchartrain across from New Orleans.

Most people bitten by an infected mosquito will not become noticeably ill, but some develop flu-like symptoms, and the weak and the elderly can get encephalitis, a potentially fatal brain infection. State and local officials have boosted mosquito-spraying efforts and urged people to protect themselves against the insects.

Encephalitis is usually seen in August and September, but Louisiana's first patients became ill in June.

The West Nile virus is showing up earlier in the summer as it moves to warmer climates, said Dr. Jim Hughes, director of the infectious diseases center at the Centers for Disease Control and Prevention.

Mississippi has 22 confirmed human cases of West Nile virus. Texas has 10 suspected cases and Arkansas one. Since 1999, the virus has been found in birds and people in 34 states and Washington, and health officials expect it will continue spreading west. On Tuesday, the first human case in Illinois was confirmed.

Gov. Mike Foster declared a state of emergency in Louisiana last week as part of an effort to obtain federal funds to fight the virus.

Two Louisiana congressmen said they received a commitment Tuesday from President Bush to help secure federal money. Democrat William Jefferson and Republican Billy Tauzin said the state needs $3 million to $5 million for more mosquito spraying.