Wednesday, March 09, 2005

Two ways to get it wrong but only one is right

It may be understandable, but it is also unacceptable. The "default assumption" is that a new case of bird flu was contracted from contact with sick poultry, to be ruled out only in the face of overwhelming evidence to the contrary. This is the reverse of the precautionary approach appropriate to such a grave public health threat.

Today Vietnam announced several more cases that were missed because they did not have the typical presentation of bird flu infection. It is significant that in both cases they are family members of confirmed cases, that is, part of familial clusters. One is an 80 year old grandfather of the two confirmed sibling cases (ages 21 and 14) from Thai Binh province reported earlier. AP (via ABC News) is also reporting that the 61 year old widow of a 69 year old man who died of bird flu on February 23 has also tested positive for the infection. Both of these new cases are reported to be in good health but have been isolated in their homes.

In each instance the reports start from the assumption that the disease cluster arose from a common source rather than person to person transmission.
Health authorities suspect that the three family members, from northern Thai Binh province, caught the virus after eating an infected goose slaughtered by the grandfather a month ago, and there was no immediate indication that they had infected one another.

Earlier this week, Vietnam reported that a 26-year-old male nurse who cared for the grandson had also been infected by bird flu but health officials said it was likely he contracted the disease outside the hospital.

Several cases in Vietnam and Thailand have involved family clusters, with several relatives were infected at the same time, though there has been no evidence that the virus has mutated into a form easily transmitted by people. Health officials warn that when that happens, the virus could spark a global pandemic that kills millions. (Irish Examiner)
Unfortunately, wishing won't make it so. The two possibilities here are that a family cluster arose from a common source, such as contact with infected poultry, or from person to person transmission. Contact with poultry in this part of the world is almost ubiquitous, so eliciting a history of such contact by no means rules out person to person transmission. The main indicator would be the timing of onset of the cases, and in each of these instances the assumed common source exposures (eating chicken, duck or goose) around the Tet holiday seems too remote to account for these cases.

Nor is it true there is "no evidence" of person to person transmission in these cases. As Henry Niman has emphasized repeatedly, the bimodal timing of onset and the period from the last known or assumed poultry contacts in a number of the familial clusters points in the opposite direction.

Underneath this is a widespread but unspoken fear among public health authorities that "raising the threat level" (to use contemporary terminology) will "unnecessarily" produce widespread fear and panic. If we are lucky enough for this to be a false alarm, the result would be a loss of credibility.

If you are looking for propositions for which there is "no evidence" I suggest you start right there. If the public trusts its health authorities (and that trust has to be earned by a history of honest communication) they will neither panic nor lose faith in them when a feared possibility doesn't materialize. I know of no evidence to show that sounding a justified alert will result in a damaging loss of needed credibility if the alert turns out to be a false alarm.

Admittedly this is a tough call for public health and there are two ways they can get it wrong: failure to warn when it turns out the warning was justified, or warning when it turns out otherwise. Using a public health precautionary approach it is clear we should be more inclined to accept the latter risk than the former, although national and international officials are tilting in the other direction. If you are going to get it wrong, it is better to err on the side of precaution than the reverse. In the US, the low key posture CDC is taking to bird flu is an unfortunate example of the wrong way to do it.

To use another well-worn cliché of the post 9/11 era, we are talking about a possible failure to "connect the dots." The dots can't get any bigger. The disconnect is at the level of responsible public health leadership.