When my colleagues announced early afternoon on Friday he was headed home because he was sick, I knew the flu had finally arrived on my doorstep. It was already here, of course. The emergency rooms are jammed, clinics have long waits and hospital admissions for flu are up — way up. The flu situation was the page one column eight story in Saturday’s Boston Globe:
The flu virus is rampaging across New England, spawning waves of coughs and fevers, causing patients to flood doctors’ offices, and raising questions about the effectiveness of flu shots given to tens of millions of Americans.
During the past two winters, the influenza season proved unusually mild in New England and much of the nation. But this year is strikingly different, with federal disease specialists reporting yesterday that virtually every state now has widespread flu activity.
“We’re seeing it raging,” said Dr. Alfred DeMaria, the top disease tracker in Massachusetts.
At Massachusetts General Hospital’s network of clinics and hospital wards, the number of patients testing positive for influenza so far this season is already 21 percent higher than for all of last winter.
At Harvard Vanguard Medical Associates, doctors report that their patients must sometimes wait an hour for care because so many people are showing up with flu symptoms.
And at Boston’s Health Department, the tally of laboratory-confirmed flu cases last week reached its highest level since the city started intensively tracking lab results four or five years ago. (Stephen Smith, Boston.com)
But you probably know this already, at least those of you in the northern hemisphere. Our many readers in Oz (Australia, New Zealand) have been through it already (see here and here). Now it’s our turn.
The season started with most subtyped influenza A viruses being H1N1. But like last year, the balance is shifting from the H1N1 subtype to the H3N2 subtype, although there is regional variation in the relative proportions of H1 and H3. H1 years tend to be milder than H3 years, so keeping track is of some interest. This year’s flu vaccine is well matched for H1N1 but not for H3N2 (see here, here), so this is not a good development. More important than the relative proportions is the sudden increase in incidence (number of new cases in a time period). 44 US states are now reporting widespread flu activity. The flu is also killing people, as it does every year:
Pneumonia and influenza (P&I) was listed as an underlying or contributing cause of death for 7.6% of all deaths reported through the 122 Cities Mortality Reporting System for the week ending February 9. This percentage was above the epidemic threshold of 7.2% for the week and marked the fifth consecutive week that P&I deaths were above the epidemic threshold since influenza activity began rising in the United States (figure 4). (CDC Update: Influenza Activity)
As the figure shows, the last two years were relatively mild. 2003 was another bad year. We still don’t know how this one will shape up, but the strain mismatch in two of the three components of this year’s flu vaccine won’t help (influenza B, the third component of the vaccine was also mismatched; flu/B accounts for about 16% of the ascertained flu diagnoses so far). On at least three measures this season is worse than any of the previous three (2004, 2005, 2006; this is the 2007 season): this year there is widespread or regional activity in 49 states compared to a high of 48 for the previous three years; this year 33% of specimens tested are positive compared to a high of 28% for the previous three years; and this year, most recently 5.7% of visits to a set of surveillance practices are for influenza-like illness, while the highest level for any week of the previous three years was 5.4%. So in comparison, this is already the worst year since 2003 and may get worse still.
A new wrinkle this year is the appearance of a mutation (H274Y) in a small proportion of H1N1 isolates thought to confer resistance to Tamiflu. So far H3N2 and flu/B are not affected. All subtypes remain sensitive to the other neuraminidase inhibitor, Relenza (zanamivir), but this drug must be inhaled and doesn’t work for systemic infections. It is also not recommended for children. Tamiflu is still recommended for prophylaxis or early treatment of influenza.
Bird flu is also flu and there is a noticeable increase in the number of reported H5N1 cases as well (see here for depiction of confirmed cases through February 5).
So far, the best summary is this: it’s flu season.