Effect Measure

Is Mexico a part of the swine flu story?

Late yesterday we summarized a CDC media briefing about the developing investigation of cases of influenza in California and Texas with a previously unknown flu virus with genetic components from pigs (“swine flu”, humans and birds). At the same time reports were surfacing of an especially virulent respiratory disease outbreak in central and southern Mexico that had resulted in 20 deaths and hospitalizations with acute respiratory failure. 137 cases have been reported, including health care workers. When asked yesterday, CDC said they were in close touch with their Mexican counterparts but at that point had no evidence of a connection.

Whatever is going on in Mexico, however, it seems to be pretty serious. Mexico’s Health Minister has ordered schools closed in Mexico City and recommended people not congregate in public places. Bloomberg’s Jason Gale has a good summary of the Mexican and American cases:

Thirteen fatal cases of severe respiratory illness were reported in Mexico City; four in San Luis Potosi, north of the capital; two in the state of Baja California Norte, bordering California; and another in Oaxaca city in the south. Most cases occurred in southern and central Mexico in previously healthy adults ages 25 to 44.

Symptoms include high fever, headache, eye pain, shortness of breath and extreme fatigue with rapid progression of symptoms to severe respiratory distress in about five days, the Canadian agency said. A ?high proportion? of cases require mechanical respiration, it said.

The four males and three females in San Diego County and Imperial County, California, and in San Antonio, Texas, diagnosed with swine flu had mild flu-like symptoms. The patients, 9 to 54 years old, included a father-daughter pair and two boys attending the same Texas school. (Jason Gale, Bloomberg News)

In addition, we know that the US swine flu variant cases also show an unusual prevalence of nausea, vomiting and diarrhea, something not mentioned in the Mexican reports. Thus the two outbreaks exhibit clinical (symptoms, severity) and epidemiologic differences (ages of cases). This doesn’t mean they are unrelated, although it makes it less likely, in my view. While the US cases are near the Mexican border, they were initially discovered because of more intense surveillance related to the Border Infectious Diseases Surveillance (BIDS) system.

It’s always difficult to make sense out of things in the early stages of an outbreak (“the fog of epidemics”), so we’ll have to await further evidence. Preliminary tests in Mexico were said to show that cases had influenza A/H1N1, influenza B or parainfluenza. The first two are the this years’ main seasonal influenza viruses. Parainfluenza is another common cause of respiratory disease. One of the major questions is whether the H1N1 is human seasonal influenza, like the H1N1 swine flu variant just reported by CDC, or something else. Since three different viruses are mentioned, we also need to know which one is the predominant virus in the current outbreak. Several news outlets report that 51 Mexican clinical specimens have been sent to the Canadian Public Health Agency laboratory for genetic characterization.

A report on Twitter from a knowledgeable source says CDC and WHO have activated their emergency response centers. That seems like a reasonable and prudent thing to do because it brings to bear additional professional resources. I don’t take it as a judgment that either agency believes this is an emergency at this point. Epidemiologists are now probably trying to develop a case definition and gather information. As they do, the picture will begin to fill in and change.

Any respiratory disease outbreak of unknown etiology with severe signs and symptoms requires immediate attention, even more so when the public is anxious. Routine assurances by authorities that “there is no need to panic” are not helpful. There is never a need to panic. Panic is always bad. You prevent it by empowering people with timely and accurate information. CDC and Canadian public health authorities have been pretty good so far, but CDC’s web portal has no obvious front page link to the swine flu page and there are no updates since yesterday’s conference call. CDC might consider setting up a special purpose blog to provide more timely and continuous information. I can guarantee that, given the stories on the newswires and flu sites already mushrooming, any information vacuum between now (10 am Eastern Daylight Time) and 3 pm will be amply filled by rumor and speculation.

While I don’t like to use this space as a news aggregator, many people come here for flu news. Since I am using the same sources as everyone else and have no special inside information, the only thing I can add is some perspective from a professional epidemiologist. I’ll do my best, realizing that this is a fluid situation and things will change.


  1. #1 Grace RN
    April 24, 2009

    Some flublog sites are already calling for the USA to go to pandemic level 6. For people who have followed the H5N1 virus and its’ potential for panflu will recognize the familiar and uncomfortable anxieties that accompany waiting for some official word versus the blogosphere’s antedotal diagnoses.

    Having following H5N1 since 1998, and especially since my local board of health’s meeting just last night, I’d have to conclude we are not much more prepared for panflu on the local level now then we were in 1998.

  2. #2 karen
    April 24, 2009

    This isn’t looking good. New Wall Street Journal Article quotes a WHO spokesperson as saying the Mexican cases are H1N1 and Reuters is quoting the Mexican Health Minister as saying on television: “It is a virus that mutated from pigs and then at some point was transmitted to humans,” he told the Televisa network.



  3. #3 D. C. Sessions
    April 24, 2009

    FWIW, I’m hearing lots of stories of a flu-like illness with higher than usual GI symptoms coming from central New Mexico. Haven’t seen that on the news yet, but it’s hardly surprising.

  4. #4 Habebe
    April 24, 2009

    revere – WHO did activate its response centre, Reuters reported that this morning:


  5. #5 revere
    April 24, 2009

    karen: The fact that some of the Mexican cases are H1N1 (and some are B and parainfluenza) isn’t a surprise. H1N1 was the predominant seasonal subtype and it is still around. So this doesn’t mean much to me in the absence of additional information. Beware of jumping to conclusions on the basis of very incomplete data. We’ll probably know more in a day or so. That’s the best we can do from where we are sitting.

  6. #6 karen
    April 24, 2009

    Thank you, revere – I can’t tell you how much I appreciate your blog & reassuring wisdom.

  7. #7 JJackson
    April 24, 2009

    The information is coming thick and fast now. As always with this kind of fast breaking new there is a significant ‘fog of war’ factor. That said the main points seem to be
    The Mexican and US cases are both H1N1(swine) – based on sequence data which is being ‘quoted’ from but not released. The sequence does not match other H1N1(swine) strains in the database.
    The sequences are sufficiently novel for the H1N1(human) component in the seasonal trivalent vax to make it ineffective.
    While these figures should be be taken with a large grain of salt Mexican authorities are assuming about 1000 cases and 20 deaths are likely to be due to this strain.
    The WHO have called for the convening of the an emergency committee under IHR(2005) presumably to review the situation and see if the Pandemic Level Indicator should be moved from 3 to 4 indicating ‘Evidence of increased human to human transmission’.
    New coverage is being translated and posted in a thread at Flutrackers if you which to ‘watch’ in real-time.

  8. #8 JJackson
    April 24, 2009

    To correct/clarify my earlier post this is not being view as a human flu (i.e. human to human transmission with no know pig contacts in any of the cases) with characteristics that show it to be of swine origin but very distinct from seasonal H1N1 strains. Mexican and US sequences are a match. What is not clear is the Ro, CAR or CFR.

  9. #9 JJackson
    April 24, 2009

    very sorry all typo that should read this IS being view as a human flu.

  10. #10 M. Randolph Kruger
    April 24, 2009

    Tossing a bit into the ring. How coincidental that Venezuela had training camps for Al Qaeda for the last 2 years. How coincident that this was limited to a 150 mile area… How coincidental that if these people in Mexico start to run they’ll will be running for the US.

    I read a report in 93 that made the suggestion that an attack by Nicaragua on Honduras and then Mexico would create a 20 million person rush into our underbelly of the US… Texas, New Mexico, Arizona, California. It would finish us as a nation from just trying to take care of them, not enough food because so much of it is produced there for here.

    Its a bit conspiratorial of course, but can we find out if that part of the Mexico City H1N1 has the same sequences as the European swine C? Smoking gun? Dont know enough to be a judge or make the call. But its amazing to me that this all happened in under a month, ended up in Texas and California all at the same time?

    Not necessarily a bit odd but right down the line on a bio-warfare attack and it is how I would do it if I were going to try. Send the agents to Mexico City, launch a bug or two then go to a public place and infect surfaces, animals or kids. Kids are notoriously nasty little buggers and infect everyone…

    Not enough information yet, but damned odd that we got no real warning cases. Just boom almost 1000 in about 19 days.

  11. #11 Mary
    April 25, 2009

    Has anyone considered Roche and other pharmaceutical companies trying to make a buck during the current recession by creating a panic to stock pile Tamiflu?
    Its happened in the movies?
    Pharmaceuticals are hurting just like the rest of us!

  12. #12 Rev. BigDumbChimp
    April 27, 2009

    Has anyone considered Roche and other pharmaceutical companies trying to make a buck during the current recession by creating a panic to stock pile Tamiflu?
    Its happened in the movies?
    Pharmaceuticals are hurting just like the rest of us!

    Lets not break out the tin foil hats so early please.

  13. #13 jim
    May 4, 2009

    frankly, a swine attack will be too low to stoop even for al Qaeda. but, now that it’s determined to be human-to-human, it may not be such a dirty idea after all. you can expect terrorist training camps to all uproot to mexico to prepare for the most base of biological attacks.