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.