LM Otero / AP file

Mosquitoes were sorted at a laboratory in Dallas County, Texas, as an outbreak of West Nile virus mounted last month.

A spike in West Nile virus infections in the U.S. this summer has strained the nation’s laboratory testing capabilities, creating brief shortages of diagnostic test kits and forcing lab staffers in some states to work extra shifts or rely on temporary hires for help.

The outbreak has surged to at least 2,636 cases and has caused 118 deaths, officials with the Centers for Disease Control and Prevention said Wednesday. Of those, 1,405 cases have been serious neuroinvasive disease infections. That ranks it as the most serious outbreak to date since the mosquito-borne virus was detected in the U.S. in 1999., said Dr. Lyle Petersen, director of the CDC's division of vector-borne infectious diseases.

The epidemic also has highlighted gaps in the system used to track and treat illness outbreaks and epidemics, experts say.

“West Nile just brought it back to us,” said Irina Lutinger, senior administrative director for NYU’s Langone Medical Center and a spokeswoman for the American Society for Clinical Pathology. “We only have limited resources to accommodate such an increase.”

In Oklahoma, two primary in-state reference labs had to halt West Nile tests briefly in late August because they ran out of kits, even as the nation’s leading commercial labs had to suspend or delay tests -- or prioritize samples of those suspected of having the most serious illnesses.

“We had a complete pause in testing,” said Kristy Bradley, the Oklahoma state health epidemiologist. “What I was surprised about is that it reached such a critical level before we were aware of it.”

In Texas, where latest figures show West Nile has sickened at least 1,127 people and caused 50 deaths, state public health laboratory staffers have been working extended shifts, including weekends and holidays. Four temporary lab workers were recently hired to help meet demand, said Grace Kubin, director of the Texas Department of State Health Services laboratory.

Neither health officials nor the makers of the tests would release figures about the number of West Nile tests performed this year compared with previous years.

However, everyone agrees that it is way up.

“I can say it’s probably doubled, easily, for the human testing,” said Kubin. Tests of environmental samples from mosquito pools, for instance, have tripled over normal levels, she said.

West Nile virus is a mosquito-borne disease that has been detected this year in 48 states. Most infected people, about 80 percent, never know they have it. About 20 percent, however, develop West Nile fever, which causes flu-like symptoms, including headache, fever, body aches, swollen lymph glands and, sometimes, a rash. Less than 1 percent of infected people develop severe West Nile disease, the neuroinvasive form of the infection, which can lead to meningitis or encephalitis. 

The outbreak is still short of the worst-ever West Nile season in the U.S.; in 2003, there were 9,862 total cases, 2,866 neuroinvasive cases and 264 deaths. But those figures included artificially high numbers inflated by one state's posting of cases of West Nile fever, Petersen said. This year's high number of neuroinvasive cases for the second week of September make it the worst outbreak to date, Petersen said.

However, he said that West Nile cases typically peak in mid-to-late August and that officials believe the outbreak is beginning to wane, especially as cooler weather approaches.

"Based on historical data, we’ve turned the corner on the epidemic," Petersen said. "We’re hopeful that the worst of the outbreak is behind us."

The shortage of testing kits manufactured by the nation’s leading provider, Focus Diagnostics, was caused largely because unanticipated demand outstripped supply, said Wendy Bost, spokeswoman for Quest Diagnostics, the commercial lab that runs Focus. The backlog is adding as much as three to five days to the turnaround times on West Nile virus tests, Bost told NBC News.

“The magnitude of the current outbreak of West Nile virus in the United States was not widely anticipated by public health authorities,” Bost said.

But Food and Drug Administration officials said they became concerned about a potential shortage of test kits in late August, when they contacted Focus and found the company had backorders of the West Nile virus IgM antibody test kit. That test determines whether a patient is acutely infected with the West Nile virus.

At the urging of the FDA, the CDC and other health officials, Focus ramped up production of the test kits, which can take weeks to produce and have a shelf life of about 24 months.

That helped avert a larger problem, said Kelly Wroblewski, director of infectious disease programs for the Association of Public Health Laboratories.

“At this point, there isn’t really a shortage,” she said. “In most cases, if stoppage had to happen at all, it only had to happen for a maximum of two days. I think it’s a supply and demand situation like anything else.”

In some states hit hard with West Nile, such as South Dakota and Mississippi, officials said they’ve managed to keep up with testing demand.

“We are not falling behind,” said Lon Kightlinger, the South Dakota state epidemiologist.

In Texas, lab director Kubin said she actually heard early that there might be a shortage of test kits and asked her supervisor to stock up.

Because there's no treatment for West Nile virus in humans, no one was denied care because of the lab test delays. With a different virus, however, any lag in testing could have slowed vital treatment, experts said. 

However, the shortage of lab techs to handle West Nile demand highlights a larger issue, said Lutinger, of the ASCP.

In the U.S., about 11,000 new lab workers are needed every year, but only 6,000 are graduating, Lutinger said. As older workers, called laboratorians, retire and fewer newcomers fill the slots, the vacancy rates in the field are growing.

“By 2018, if more students and second careerists are not recruited to become laboratory professionals, the shortage could be as high as 18 percent in areas such as blood banking,” she said.

About 70 percent of doctors’ decisions are based on the outcome of lab analysis, Lutinger noted.

“At a time of critical importance of providing diagnosis and test results to arm these physicians with these results, we frequently face the challenges of being unable to have trained technologists,” she said.

Too few lab workers may mean delays in diagnosis and treatment of disease – and slower response to large-scale public health crises, such as the 2009 H1N1 flu pandemic.

“It certainly has the potential to hinder our ability to respond in emergencies,” said Wroblewski.

Part of the problem may be that it’s a low-profile profession, so not many students consider becoming laboratory technologists, she said. The starting pay for public labs can be moderate, about $40,000 to $50,000 a year, and commercial labs may steal workers away by paying up to 50 percent more.

That presents a challenge for public health labs, as the current West Nile outbreak demonstrates.

“If the projections of the ASCP are correct and this continues to be a problem for the next several years, the situation of public health labs being in a good position could change,” Wroblewski said.

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