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Swine influenza H1N1 update

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pandemic-phase-42Here are some updates on the global status of swine influenza H1N1.

As of Monday, 27 April, the US has reported 40 laboratory confirmed cases of swine influenza H1N1 infection in California, Kansas, New York City, Ohio, and Texas. Mexico has confirmed 26 human cases with seven deaths,  Canada reports six cases, and Spain one case. The first two cases of the illness in the UK were reported in Scotland. These statistics were obtained from ProMED-mail, WHO, and CDC.

You might find higher numbers from other sources. The difference is that the numbers in the preceding paragraph are laboratory confirmed cases – meaning that the virus has been isolated from the patient and identified as swine influenza H1N1 (or A/California/07/2009 (H1N1), in the influenza virus nomenclature). Many suspected cases are being reported – in these the disease appears to be influenza, but confirmation of infection with A/California/07/2009 (H1N1) has not been confirmed by laboratory tests. For example, the suspected death toll in Mexico is 149, with 1995 hospitalizations. There are also suspected cases in England and Australia.

As a consequence of the continuing spread of the virus, the WHO Director-General has raised the level of influenza pandemic alert from phase 3 to phase 4. According to WHO, “This phase is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause community-level outbreaks.” A complete explanation of pandemic alert phases can be found at the WHO website. In Mexico, health authorities have closed schools in the entire country until 6 May. In the US, CDC activated its Emergency Operations Center to coordinate the agency’s response, and the Secretary of the Department Homeland Security has declared a public health emergency. These actions will allow the release of funds to support the public health response.

Because a vaccine is not yet available for A/California/07/2009 (H1N1), antiviral compounds (Tamiflu and Relenza) must be used to curb epidemics. The use of such compounds may save many lives at the expense of selecting for drug resistant viruses. If such variants emerge before immunization can be carried out they will limit our ability to control the infection.

Here are my answers to some questions posted to virology blog:

Q: Do you have any theories as to why the mortality rate (apparently) is higher in Mexico than it is elsewhere?

A: I have two theories. One involves the possibility that infection with the current circulating human H1N1 strain might confer some protection, in the form of milder disease, to infection with the swine H1N1 virus. If this is true – and it might not be – then one could speculate that individuals in Mexico City were less immune to human H1N1, and consequently experienced more severe disease when infected with the swine strain.

The other theory is more vague – because Mexico City is extremely densely populated, the virus may spread more quickly, infecting more people, leading to selection of more virulent viral variants.

Q: Are viruses more likely to get more or less pathogenic as time goes on?

A: It could go either way. Viruses need living hosts in which to multiply – if they kill the host quickly, or debilitate the host so it cannot interact with others (to spread the infection), then the virus will not endure. On the other hand, you can imagine how increased virulence leading to more coughing and sneezing could help spread the infection. This topic is hotly argued among virologists, which means that both sides probably are correct.

Q: Should we be saving our Relenza and Tamiflu if this does become highly pathogenic?

A: Save them for the fall, in case the virus returns then. Flu season is basically over in the US, and with the increasing heat and humidity (over 90° today in NYC) virus transmission should soon stop. However, if A/California/07/2009 (H1N1) takes hold in the southern hemisphere in the coming months – their flu season is still beginning – it is likely to return to the northern hemisphere in the fall. Unfortunately, by then extensive antiviral use in the southern hemisphere is likely to have produced drug-resistant variants.

Q: I keep thinking about the Great Influenza book – that in an era with no planes, the virus traveled around the world three times. Given our capacity for travel now, is quarantine even possible?

A: No. The CDC has already said quarantine is futile. Check out the transcripts of their press conferences; they are a good read (or listen).

Q: Will our over vigilance in treating this lead to its becoming resistant quicker?

A: If you mean treating the infection with antivirals, then the answer is a resounding yes. Many people have likely been saving Relenza and Tamiflu, and they will take them at the first sign of a respiratory illness.

Q: Should this be considered a prime candidate for next winters flu season?

A: It depends on what happens in the southern hemisphere. In the next week or two we will know whether A/California/07/2009 (H1N1) spreads in the lower half of the globe and causes epidemics of disease. If it does, then it is highly likely that the virus will return here in the fall. If the virus fails to spread, then everyone can go back to worrying about H5N1.

Send your questions to virology blog (virology@virology.ws) and I will post my answers each day.

Reader Interactions

Comments

  2. Your influenza nomenclature is incorrect. Strain designation for human viruses is as follows:
    Influenza type/Country/isolate number/year (subtype is in brackets)
    For example, one of the swine flu viruses from California is:
    A/California/09/2009 (H1N1)
    Dr. Ben Johnson
    Imperial College London

  3. “The other theory is more vague – because Mexico City is extremely densely populated, the virus may spread more quickly, infecting more people, leading to selection of more virulent viral variants.”

    Selection…as in virus that makes people sicker produces higher virus load that increases spread?

  4. Excellent analysis as always, Vince. I have a third theory about why fatalities could be higher in Mexico City: that town has some of the worst air quality in the world. I'm just speculating here, but it seems at least plausible that high smog and particulate pollution levels could tip some patients over the edge, turning an unpleasant but otherwise survivable case of the flu into a deadly viral pneumonia.

  5. Hi Vince–with respect to differences in mortality/pathogenesis between Mexico and the US, what about the extent of vaccination? Certainly there's a big push in the US to get regular vaccinations. Those who have been vaccinated have had multiple exposures to other H1N1 viruses.

  6. In line with Dr. Doves comment:

    You mentioned in a TWiV that a theory about the mortality in the 1918 influenza stemmed from a concurrent infection with a bacteria that weakened the bodies immune response. Is that a possibility here? I only ask because you mentioned people living in such close proximity–already present flora in the lungs+pollution+new viral infection?

    Or could there be another virus, in addition to H1N1, causing an additional immunological insult?

  7. There has been no mention, save a passing comment from the media on pneumonia, of the pathology associated with this influenza pandemic. Could it be necrotizing bronchial interstitial pneumonia or is that only associated with H5N1? What about MODS or Cyanosis? What, essentially, is killing our Mexican neighbors?

  8. I agree. Just saying 'death' is astoundingly vague. It would be good to know some more details. It seems though like if it was multi organ system failure we would have heard at least that by now.

  9. How about the delay in access to quality health care or laxity on the part of patients to seek treatment as they ignore the symptoms of early disease just as another case of “cold”?
    Combine it with secondary bacterial infections and/or high pollutant levels and low immunity levels as eluded to by Vince, hence high mortality!

  11. Regarding your first theory of why the non-Mexican cases are milder:

    “…infection with the current circulating human H1N1 strain might confer some protection…”

    I'm just a layman, and so I'm wondering exactly how something like that would work. What percentage of (say) American victims would likely have this benefit? Enough to explain the discrepancy? Why wouldn't we expect a similar number of “protected” persons in Mexico?

    Also, regarding the “air pollution theory”, haven't their been deaths inside Mexico, but outside Mexico City? Perhaps in locales with comparatively pristine air?

  13. Here's a new question for your next Q&A session:

    A New Zealand blogger posits that getting swine flu now could be beneficial if this becomes a pandemic. (“How Swine Flu Could Save Your Life” – http://aardvark.co.nz/daily/2009/0428.shtml) Clearly, he makes some poor leaps of logic (assuming that the “young” mentioned in his influenza.org quote means “young adults” and not children / babies with less exposures), but he presents what seems to be a reasonable point re: cow pox and small pox….

    A) Could getting the swine flu now help to weather future, more virulant strains?
    B) Since this flu also has a bird flu heritage, could catching (and surviving) it help with a possible H5N1 outbreak in the future?

  14. I am from mexico, and Yes there have been death in the states outside mexico city. In fact the first cases of infection and death were registered in states different from Mexico city.

  15. HI THIS IS MY FIRST TIME I AM FROM BOLIVIA I AM INFECTIOUS DISEASES DOCTOR AND FIRST FOR BEN JOHNSON THE NOMENCLATURE IS OK BECAUSE THE VIRUS WAS ISOLATED FIRST IN PIGS THAT IS WHY IT IS COMMON NAMED SWIN FLU LIKE H5N1 BIRD FLU.
    OTHER ALL OF US WILL GOING TO BE IN CONTACT WITH THE VIRUS IN THE NEXT MONTHS OR YEARS WHAT IS THE BEST TO GET SICK NOW OR LATER I THINK WE MUST RESIST ALL WE CAN BECAUSE I THINK ON DECEMBER THE VACUNE COULD BE DISPONIBLE (BUT A FEW PEOPLE WILL BE ABLE TO GET IT) WE WILL KNOW MORE ABOUT THE VIRULENCE AND PATHOGENECITY THE POSIBBLE RESISTENCE TO NEUROAMINIDASE DRUGS OR DE USEFULNESS OF OTHER (RIBAVIRIN, CLOROQUIN),ALSO THE VIRULENCE MIGHT BE OR NOT LOWER THAN AT THE BEGININ….THESE ARE MY REASONS.

  16. I'd like to know the potential lethality of swine influenza as compared with other types of influeza viruses. IS THERE ANY REFERENCE ABOUT THE RISK OF INFECTION IN OPEN OR CLOSED SPACES??
    tHANKS

  17. how long would you expect human immunity to exist within an individual infected with h1n1 virus?

  20. This strain of influenza appears to be no more lethal than recent
    seasonal influenza strains. Transmission in closed spaces is always
    more efficient than in open spaces.

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  25. In general, the majority (about 90%-95%) of people who get the disease feel terrible but recover with no problems, as seen in patients in both Mexico and the U.S. Caution must be taken as the swine flu (H1N1) is still spreading and has become a pandemic. So far, young adults have not done well, and in Mexico, this group currently has the highest mortality rate, but this data could quickly change.

  26. In general, the majority (about 90%-95%) of people who get the disease feel terrible but recover with no problems, as seen in patients in both Mexico and the U.S. Caution must be taken as the swine flu (H1N1) is still spreading and has become a pandemic. So far, young adults have not done well, and in Mexico, this group currently has the highest mortality rate, but this data could quickly change.