by revere, cross-posted from Effect Measure

In the US we are about to embark on the Thanksgiving holiday, a 4 day period where families get together for a celebratory meal (at least celebratory unless you are one of the original inhabitants of the continent). There is lots of intergenerational visiting (grandparents to great grandchildren and lots of mingling of people from disparate geographic areas). In the midst of a swine flu pandemic, the obvious question is the epidemiologic implications. Ordinarily there is some effect. Ordinarily.

Thanksgiving is typically followed by at least a modest bump in early seasonal flu cases, according to reports from the past few years. But this, of course, is not a typical year. Swine flu is a new virus that accounts for nearly all flu cases right now. (AP via MSNBC)

Not a typical year indeed. We’ve already had as much or more flu at a time by which we usually have recorded little flu, although the flu is in a portion of the population unused to bearing the brunt. So what are the issues here? We’ve already mentioned some of them.

Thanksgiving festivities produce two things of epidemiological import. There are increased close contacts between different age groups (for example elementary, highschool and college age and the over 65 age group); and close personal contacts between people from widely separated geographic areas. It’s a heady mix. December is the time when seasonal flu starts, slowly at first, then picking up steam in January and February. But this year we’ve already had a whole flu season (and more), although the usual victims (old folks like me) have so far been spared the worst. Will it now be our turn, falling prey as we usually do to seasonal flu? Or has the new kid on the block, swine flu, in some way we don’t quite understand, “crowded out” the usual residents? We don’t know yet.

There’s also a new and completely different mix of the susceptible and immune in the population, a vaccination campaign targeting younger populations just starting to get underway, weather turning colder (which increases flu in ways we don’t understand) and a major economic recession that is affecting habits, living patterns and perhaps susceptibilities in unknown ways. The dynamics of seasonal flu — how the disease unfolds in space in time — still isn’t understood and now we have a completely novel situation: not only the aforementioned factors, but possibly four flu viruses (swine flu, two seasonal influenza A subtypes and influenza B) all circulating — maybe — along with the usual other respiratory viruses (respiratory syncytial and rhinoviruses chief among them).

What will be the result? We’re going to find out soon.