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Don’t rely on quick flu tests, CDC tells doctors

A sign advertising flu shots is displayed at a Walgreens Pharmacy on January in Concord, California.
A sign advertising flu shots is displayed at a Walgreens Pharmacy on January in Concord, California.Justin Sullivan / Getty Images

Flu is now widespread in 41 U.S. states, and as patients fill clinics and emergency rooms, federal health officials are advising doctors not to rely entirely on quick flu tests.

The H1N1 swine flu — which first emerged in 2009, when it caused a pandemic — is causing 99 percent of the cases that are being tested, the Centers for Disease Control and Prevention said in its weekly flu report.

It’s not clear why, but the rapid flu tests used in many clinics are getting what are called false negatives — that is, they indicate someone does not have influenza when in fact they do, said Dr. Angela Campbell, a medical officer in CDC’s respiratory diseases branch.

Because flu can kill — and rapidly sometimes — doctors, nurses and other health professionals should be treating patients based on symptoms, Campbell told doctors on a conference call this week. The flu drugs Tamiflu and Relenza can both ease symptoms, but they work best when given quickly, within a day or two of symptoms showing.

The false negatives are worrisome because H1N1 seems to pick on people who don’t usually get the sickest with the flu — younger adults.

“CDC has received several reports of severe illness in young and middle-aged adults, including pregnant women and people who are obese,” CDC said. Usually flu hits hard in people who are over 65, very young children, and people of all ages with other conditions such as asthma or diabetes. But H1N1 is different and health professionals need to be ready to treat people even if the first flu test comes up negative.

There are more precise flu tests, but they can take a day or two to come back and that’s valuable time to lose when quick treatment is important. Patients with respiratory distress, pneumonia and other severe symptoms probably should be treated for influenza if it's circulating.

Dr. Janet Diaz of the Contra Costa Regional Medical Center in Martinez, Calif., said on the CDC flu call that many of their sickest flu patients have been women with an average age of 43 — not the typical group doctors usually expect to see in the hospital with influenza. Most were obese, but not extremely so.

Morbid obesity — in which people have a body mass index or BMI of 40 or higher — can put people at higher risk of flu complications.

Every year, flu kills anywhere between 3,000 and 49,000 people in the United States, CDC says. It puts 200,000 or more into the hospital. An estimated 50 million people get flu every year, CDC says.

So far this year, flu has killed 28 children. CDC doesn’t keep a precise count of adults killed by flu, and it can take a few weeks for reports of deaths to come in.

Campbell said Americans can expect to see flu active for at least a few more weeks. It’s not too late to get a flu vaccine, which CDC says is the best way to protect against influenza. CDC advises everyone over the age of 6 months to get a flu vaccine every year.

Just this week, a team of researchers said it's possible that using certain cold medicines to reduce fever and help people feel a little better could be spreading flu more widely, because people who feel better are more likely to go out and spread their germs. 

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