It’s been a meteoric rise to infective fame for the recently discovered swine flu virus H1N1, as the number of confirmed cases here in the United States has risen to 109, and the World Health Organization (WHO) on Wednesday raised the pandemic alert level to Phase 5.
As scary as it sounds, the new designation only confirms what we already know: Humans don’t need contact with swine to catch this version of the swine flu. Phase 5 indicates widespread human infection, defined as human-to-human spread of the virus into at least two countries in one WHO region. Phase 6 is the global pandemic phase, with community-level outbreaks in at least one other country in a different WHO region.
Initially it was only travelers to Mexico who might have felt an anxious tickle deep in the throat, or some mild muscle aches, and wondered. Then it was time for anyone who wasn’t feeling well and who had recently traveled to one of the three, or six, or 10 states with confirmed cases to get a little nervous. Now with confirmation of the state’s first swine flu case, Minnesotans can look out the window and know that the virus has arrived.
Defining a ‘suspect case’ and who needs to be tested
Evidently the Minnesota Department of Health (MDH) can measure the public’s anxiety level by the number of requests it receives for individual swine-flu testing. On Tuesday the MDH issued a notice to physicians detailing exactly whose sputum sample it’s interested in evaluating — ie. what constitutes a suspect case.
MDH is using the Centers for Disease Control and Prevention’s (CDC) definition of a suspect case: “A person with an acute respiratory illness who had close contact with a confirmed or suspect case of swine influenza A (H1N1) virus infection while the case was ill OR a person with an acute respiratory illness who traveled to an area with confirmed cases of swine influenza A (H1N1) within 7 days of suspect case’s illness onset.”
The required exposure seems clear, but I was a little puzzled by their definition of “acute respiratory illness”: rhinorrhea (runny nose) or nasal congestion, sore throat, cough, fever or feverishness. As a physician, that list sounds to me more like the common cold than influenza, which typically presents as a high fever, headache, severe muscle aches and fatigue, with a dry scratchy cough and a sore throat.
I asked Dr. Frank Rhame what he thought about the CDC’s definition of a suspect case. Rhame is an adjunct professor in the infectious disease section of the University of Minnesota School of Medicine and an adjunct associate professor in the epidemiology division of the University of Minnesota School of Public Health. He’s also research director at Abbott Northwestern Hospital’s Infectious Disease Clinic.
“If you went to a particular area of Texas and came back with a cold, they want your nasal secretions,” is how Rhame summarized it.
“Right now they’re trying to get a handle on what is going on. They want a broader definition,” Rhame continued. “Just a cold shouldn’t constitute a suspect case of swine influenza. You have to have a cold, plus exposure to be a suspect case. The health department, for purposes of collecting specimens, is trying to cast a relatively broad net.”
Influenza A patients’ samples sought
As a part of that net, MDH is requesting respiratory secretion samples from anyone who has tested positive for influenza A, even if the patient doesn’t fit the definition of a suspect case. (The admonition “Please do NOT send specimens to MDH-PHL for swine influenza testing unless one of these criteria has been met,” gives one a sense of how many requests the department has received.)
But how good are the screening tests — a swab of the nose or throat — that we use in clinics or emergency rooms to detect type A influenza (all swine flu strains being type A)?
“It looks like the sensitivity of the standard in-office rapid flu test is not very good for this virus,” Rhame told me. Where these screens fail to detect the standard flu viruses in 10 percent or more of cases, according to Rhame, it’s even worse for the swine influenza virus, in the range of 30 percent. In other words, if an office test is positive for influenza A, then you MIGHT have swine flu, but a negative test can’t rule it out.
Is summer on our side?
It’s still not clear how virulent this strain is, and how far it will go geographically and chronologically. But the epidemiology of influenza suggests that we have summer on our side.
“The big question here is whether this virus is going to behave like influenza viruses usually do. That is to say, sort of disappear along about April or May, and not resurface until November, December, or January,” Rhame said.
We’re able to dismantle a virus into individual gene sequences, but we still don’t understand why influenza is a winter disease.
“There are a lot of hypotheses about that, but no real understanding,” Rhame told me. Are there any leading guesses? “The density of people; air exchange rates — when your windows are open the air in your house turns over faster; weather things like humidity — those are some ideas, but no one really knows.” Still, the timing of this current outbreak makes Rhame a bit nervous.
“It’s been informally reported in the Mexican epidemiology that they saw an increased number of cases in April, so that’s not the tail-off of cases that you usually see in March, April, May,” he explained. “If this swine influenza virus has got a shoulder, that’s cause for concern. You’d really like to see it winding down. If it’s winding up, that’s something to worry about; it might mean that somehow, contrary to all influenza behavior in the past, it’s not going to disappear in the summer. I sure would like to see some indication that it is tailing off.”
Mucus droplets and airborne mists
Influenza is spread in the respiratory secretions that infected persons cough or sneeze up. Larger droplets can travel 5 or 6 feet, and viruses inside these droplets can remain viable for as long as eight hours. Aerosolized droplets are thought be less effective at spreading disease because they contain lower numbers of viruses, and they dry out much more quickly. So typically the most prominent mode of transmission is snot-to-hand-to-hand-to-nose, with aerosolized droplets being inhaled into the nose being second.
“The relative importance of those two, I would say, is uncertain for this swine influenza. The problem with this outbreak is that you’ve got a virus that has moved this far this fast in six weeks, and to imagine that that’s all by hand transfer as opposed to some airborne spread seems to me a stretch,” Rhame told me.
“There have been some epidemics that provide very strong evidence that influenza virus can transmit in the true airborne fashion, that is to say, staying in the air a long time, and going a long distance,” he said.
In search of a vaccine
The CDC reports that a team is working on being able to culture the virus, the first step toward creating a vaccine against it. The decision as to what three flu strains will be included in next year’s flu vaccine is typically made in February. That’s because the process currently used to produce vaccine is lengthy and ridiculously antiquated (a commonly expressed opinion before this current outbreak). The process involves cultivating the virus inside of live chicken eggs and then putting them through an extraction and purification process.
Rhame feels confident that it isn’t too late. “I can guarantee you that a representative of this strain will be available in the fall, I guarantee you,” he assured me. “The production system is still as antiquated as ever, but they’ll figure it out.”
While we wait for warmer weather and a vaccine to knock this swine flu strain down and hopefully out, we’ll need to rely on smart public-health measures and the finely tuned minds at the CDC and MDH. And good hand washing.