It’s getting a little frenzied out there, what with the Centers for Disease Control and Prevention and the State Department making noises about travel bans to Mexico. Not that there isn’t cause for concern, but so far, this looks like a good practice run for early detection and intervention in an epidemic — practice countries will no doubt need on a grand scale in the future.

As always, when I want to get the true skinny on what’s happening with infectious diseases, I check with the moderators at ProMed, a service of the International Society of Infectious Diseases. They tend to A) stay calm and B) offer perspective in detached medical-ese:

The media feeding frenzy is very reminiscent of the early days of SARS — an apparently highly contagious novel viral febrile respiratory infection cropping up in multiple locations, with many unknowns as to the origin of the virus and what will happen next.

To summarize the status of confirmed cases and suspected cases as best as one can (given the exponential growth of press releases and press interviews leading to thousands of newswires): There are presently 20 confirmed cases in the United States involving 5 States — California (7), Kansas (2), New York City (8), Ohio (1) and Texas (2). Of these, only one has been hospitalized and all have been relatively mild and self-limited infections. There have been no fatalities attributable to this novel H1N1 virus infection in the USA reported as of today (26 Apr 2009).

In Mexico there have been over 1400 reported cases in 19 of 32 States, with 81 (or 86 depending upon the source) reported fatalities. There have been 6 cases confirmed in Canada, 4 in Nova Scotia, 2 in British Columbia — all 6 cases have been mild with self-limited illnesses.

Any individual with a history of travel to a location with known confirmed cases of the H1N1 virus who develops an influenza-like illness is considered a suspected case

In addition to the confirmed cases in North America, there are suspected cases reported from New Zealand, Spain, France, Israel — all involving travelers returning from Mexico. At this point in time, any individual with a history of travel to a location with known confirmed cases of the novel H1N1 virus who develops an influenza like illness (ILI) is considered a suspected case until results from laboratory testing are available. One would expect the volume of reports of suspected cases to grow, as more and more travelers return to their countries of origin, with a proportion of them having ILIs — a well-observed illness following airline flights.

In an earlier posting, this moderator pointed out that the reported cases in Mexico were hospitalized pneumonia cases, with surveillance data coming from inpatient facilities. In contrast, the information on the reported cases in the USA involved surveillance data coming from outpatient facilities. This difference in sentinel reporting sites biases reported cases in Mexico to be more severe cases as they are cases that were severe enough to merit hospitalization.

In turn, the use of outpatient sentinel surveillance sites in the USA leads to a bias selecting milder cases — those that do not require hospitalization. One suspects that once the countries heighten ILI surveillance to include both inpatient as well as outpatient facilities, these disparities will lessen. One also suspects that the true number of cases in Mexico is significantly higher than the currently reported approximately 1,500 cases, which would further lower the calculated case fatality rate (CFR).

Based on the currently available information, the novel H1N1 virus involved in these outbreaks has genetic material from human viruses (permitting human to human transmission), avian influenza viruses, and swine influenza viruses. For years the scientific community has been speculating that new influenza strains might arise when an avian influenza virus infects swine that are also coinfected with human influenza viruses. This coinfection in the same host, along with a possible 3rd coinfection of a swine influenza virus, has been felt to offer the potential for reassortment of the genetic material of the viruses, that might ultimately produce a virus that is novel to humans, and can infect humans and be transmitted between them.

Now for the conspiracy theories ….

If I were more paranoid or even more cynical, I’d wager that it was no accident that the swine flu outbreak occurred in densely populated (and not overly clean) Mexico City. I would also speculate that the combination of swine, human and bird influenza viruses into one super-virus was probably no accident, though scientists have been saying for years that the pandemic virus probably would arise from a recombinant virus just like this.

So, was it al Qaeda? The Chinese? Some evil genius mad scientist? No, it was probably God, since God made everything.

For the past four years, Mexico has battled the H5N2 strain of bird flu — the one that can’t be passed on to humans — throughout large areas of the country’s south and center. So there was ample opportunity for bird flu to mix with swine flu, which opened the door to human infection (as viruses are transferred rather easily between pigs and humans). So there you have it — God futzing around with genetic material in the Petri dish of the universe just to see what will happen and what we will do about it.

I, for one, intend to follow the CDC’s advice on this one — wash hands, wash hands, wash hands.