(The New York Times News Service) -- Houston-area doctors rarely test for West Nile disease, even in patients hospitalized with brain inflammation that can be caused by the West Nile virus, according to a new study.

The study found that local doctors who treat patients with meningitis and encephalitis routinely discharge them without knowing the disease's cause, likely often West Nile. It found that doctors usually only order tests for bacterial and fungal infections, historically considered the greatest threat.

"It's no wonder that we don't have a diagnosis at discharge so much of the time if we're not doing the available testing," said Dr. Rodrigo Hasbun, a professor of infectious disease at the University of Texas Medical School in Houston and the study's primary investigator. "Doctors need to integrate viral tests too."

The study, which looked at data from nine Memorial Hermann hospitals between 2005 and 2010, found only 11 percent of meningitis and encephalitis patients were tested for West Nile after doctors ruled out bacterial and fungal infections as their disease cause. In all, 72 percent of meningitis and encephalitis patients at the hospitals were discharged without a cause of the disease.

Hasbun said he guesses doctors only rarely test for West Nile in meningitis and encephalitis cases because no treatment for the virus exists and because doctors are so focused on bacterially caused cases, which kill the patient roughly 30 percent of the time. By contrast, the enterovirus - the virus that most frequently causes the two brain conditions - usually results in benign outcomes.

But Hasbun noted that neuroinvasive West Nile, the term for meningitis or encephalitis caused by the mosquito-borne virus, has a death rate of about 10 percent and also often cause serious long-term disabilities. He added that more extensive West Nile testing is necessary for the study of the disease, to determine its size and patterns.

Hasbun said he was surprised by the study finding, but Dr. Kristy Murray, a former colleague of Hasbun's now at Baylor College of Medicine, said it's consistent with her recent study attributing kidney disease and other chronic conditions to West Nile infections patients had contracted years before. She said most of those patients had to fight to be tested for West Nile or only got the test years after, as their symptoms persisted.

Hasbun and Murray said they think such "under-testing" is likely occurring around the nation, not just in Houston.

The study, not yet published, comes amid a West Nile outbreak that is the worst ever in Texas and one of the nation's worst ever.

Hasbun decided to release the study results, before publication, because of public health implications. He said the findings show that the numbers being reported only scratch the surface of the actual amount of West Nile infecting people.

Of the small fraction tested in Hasbun's study, 43.5 percent had neuroinvasive West Nile.

Only about 1 in 150 people infected with the West Nile virus develop neuroinvasive West Nile. Roughly 1 in 5 infected people develop West Nile fever, typically characterized by mild symptoms such as headaches, joint pain, fever, skin rash and swollen lymph glands. Testing for it is even more rare than neuroinvasive disease.

Eighty percent of people infected with the virus develop no or few symptoms.

Hasbun's study found 69 of 628 meningitis or encephalitis patients were checked for West Nile after tests found their spinal fluid negative for bacterial and fungal infections. The 628 patients include 97 children admitted to the hospital between June and October when West Nile is circulating and a very likely suspect. Fifteen of those children were tested for West Nile.

The remainder of the patients, adults, were admitted to the hospital at all times of the year. Hasbun hopes to soon have a breakdown of those just admitted during West Nile season.

Hasburn, who undertook the study because of frustration over the number of meningitis and encephalitis patients being discharged without a diagnosis, said his follow-up research will include looking for undiscovered viruses that cause the two conditions.

todd.ackerman@chron.com

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