Okay, everyone's really tired of hearing about the flu now. And many of us have been, or still are, sick as well as tired. But the latest weekly numbers have been published, and flu season still could have a few months to go. Though the disease has likely peaked now, public health officials and epidemiologists say its epidemic status is still with us.
"Elevated" is the word that the Centers for Disease Control used to describe flu risks in every region of the country at the last reported date (week 4 of 2013, or about halfway through the official season). The full force of the disease finally hit California. The national "Elevated" level means that flu risk is at or above baseline for all 50 states, the District of Columbia, Guam, Puerto Rico, and the U.S. Virgin Islands.
Over the course of the season, the main flu viruses circulating among the population vary by state and by region. A noninfluenza week is a week during which less than 10% of specimens collected from clinic or hospital cases test positive for influenza.
This year's reported influenza viruses
Only a quarter to about 40% of patients with flu-like symptoms are actually proven to have an influenza virus. Since October 1, 2012, CDC has identified more than 900 viruses collected in the U.S. that cause flu.
At least five main groups of viruses among the total 920 have been identified so far:
- 556 influenza A/H3 viruses (the most common throughout the year, about half the type A total), comprising two strains:
- Victoria/361/2011-like
- Another A variant, not yet subtyped but found in numbers similar to A/Victoria
- 66 influenza A/H1N1 (California/7/2009-like viruses),
The 2009 pandemic A/H1N1/Caliifornia virus, a swine flu, contained a combination of gene segments that had not been reported previously in either animals or humans. Although a variant of it was implicated in the "Spanish" bird flu pandemic almost 100 years before, because most people had no preexisting antibody to this strain, the H1N1 virus could spread rapidly four years ago.
- and 298 influenza B viruses (two strains).
Influenza B viruses undergo antigenic drift (mutation) less rapidly than influenza A viruses. Currently circulating influenza B viruses mainly come from two distinct genetic lineages: Wisconsin (Yamagata), and Victoria. Both types of influenza B viruses have circulated in most of the recent influenza seasons. To date, this year has seen over twice as much B/Wisconsin as B/Victoria.
Flu protection in this year's shot / Effectiveness of antiviral medications
Pharmaceutical manufacturers included these three strains in this year's flu shots:
- A/Victoria,
- A/California/H1N1(2009), and
- B/Wisconsin.
As I noted above, all three have actually shown up in the population. The once-potent A/California/H1N1 is still around after four years, but in much lower numbers than before (less than 3% of the A viruses this year).
Tamiflu(R) (oseltamivir) and Relenza(R) (zanamivir) have both been found fairly effective this year in helping early flu sufferers reduce the effects and duration of the disease. Both are neuraminidase inhibitor medications used in the first 24-48 hours of illness. Physicians especially recommended them when patients with confirmed or suspected influenza also have another severe, complicated, or progressive illness, require hospitalization, or are at greater risk for serious flu-related complications.
Nationwide flu activity: 1st 4 weeks in January
In week four (January 20-26, 2013) of the 2013 segment of this flu season, influenza activity remained elevated in the United States, but its effects had decreased in some areas. The risk now is about as high as it was the second full week in December--or a little less than half as bad as it was at its recent peak just before New Year's.
Most of the country is still experiencing widespread flu (see map). In many of the deep South states and part of the northern Plains, the flu is regional but not as dominant. Hawaii and the District of Columbia are experiencing mainly local outbreaks.
Nationwide, hundreds of thousands of people, possibly more, have had influenza this season. At least 75,000 had medical visits or hospitalizations for influenza and related pneumonia, and 45 children have died of flu or its complications since September 2012 (many more adults, although the government keeps official death records only for children, the main carriers of the disease.)
The seasonal outbreak of 2012-2013 continues to harm seniors, who get somewhat less protection from flu shots than younger adults. (It's still important for seniors to be vaccinated, because more of them get serious flu or die from the disease.) About half of the influenza-associated hospitalizations reported this season have been among people 65 and older.
The most commonly reported underlying medical conditions among hospitalized adults: cardiovascular disease, metabolic disorders, obesity, and chronic lung disease (except for asthma). About half of children hospitalized so far have had no identified underlying medical conditions.
ScienceDirect estimates the average cost of a recent annual influenza outbreak in the U.S. at over $80 billion. Considering these costs and the possible consequences (including side-effects and medical error as well as disease prevention), for most of us a flu shot is an excellent investment.
Based in Chicago, Sandy Dechert has been covering the 2012-2013 influenza epidemic for Examiner.com. She reports other top health news as well, including the fungal meningitis outbreak, West Nile virus, other threats to the public health, and unusual case histories like Aimee Copeland's necrotizing fasciitis.
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