Is San Diego headed for a big flu season?

Australia, which often serves as a sneak peek of America’s flu season, is coming off a significant bout of influenza-related illness just as cases are starting to spike in San Diego.

Does this mean that we’re in for an extra achy winter?

Dr. Wilma Wooten, the county’s public health officer, says its too early to tell for sure.

“We don’t have enough information yet to tell how severe the flu season is going to be,” Wooten said.

Still, the picture is growing more clear by the week. The county’s latest influenza report shows that there have already been three times as many confirmed flu cases than there were last year.

The 384 cases confirmed so far are four times the three-year average. And, the percentage of people showing up in emergency rooms with flu-like symptoms doubled in a week, jumping from 1 percent to 2 percent of all ER cases. However, that rate equals last year’s rate and remains a percentage point lower than the average over the last three years.

Australia, with its mirror-image seasons, just exited its winter flu season with 2.5 times as many cases as it usually sees, according to the most recent Australian Influenza Surveillance Report.

Dr. Robert Schooley, chief of the Division of Infectious Diseases at UC San Diego School of Medicine, said the down under connection is real but imperfect.

“Certainly there does seem to be more cases, and it’s also true that, in general, things that happen in the southern hemisphere are more likely to happen in the northern hemisphere, but that’s not always the case,” Schooley said.

There are so many variables that affect how the flu virus spreads that it’s impossible to know for sure if Australia’s flu experience this year will be repeated in the Northern Hemisphere even though the viral strains in circulation are usually the same.

Even if the flu does end up infecting large numbers in San Diego this year, Schooley added, it’s important to keep things in context. The worst seasons tend to occur when a “novel” flu strain appears and spreads. That’s just what occurred in 2009 with H1N1 influenza. First detected in the state of Veracruz, Mexico, the first case in America was a child in San Diego County.

Because the virus was not one of several included in that year’s flu vaccine, infections spread rapidly, eventually reaching pandemic status, a category reserved for epidemics that infect populations worldwide.

Researchers determined that the version of the flu virus responsible for filling local emergency rooms in 2009 crossed over from pigs which are a known natural reservoirs of influenza virus.

This year has seen several similar strains pop up in the United States. A report from the U.S. Centers for Disease Control and Prevention documents three cases of novel flu in Colorado, Nebraska and Michigan. Two of the three were exposed to swine in the week preceding illness.

While any new strain of the flu virus is important to keep an eye on, most don’t turn into pandemics. The CDC didn’t even start its current program that looks for new flu strains until 2007.

“I don’t know that these novel cases are something to be weeping out the window about, but it is something that we have to pay attention to,” Schooley said.

The nation’s viral surveillance labs, including the one in San Diego, regularly analyze flu samples from patients who visit designated “sentinel” hospitals to determine if novel strains are present.

“If there was a novel strain then it would show up in our process just as it did back in 2009,” Wooten said.

The county recommends vaccination to help control the spread of flu through the community this season. All local health providers give flu shots, and the county has special clinics for those without health insurance. Call 2-1-1 to find the nearest clinic.

paul.sisson@sduniontribune.com

(619) 293-1850

Twitter: @paulsisson

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