H5N1--does it live up to the hype? Redux

Okay, one more quick post. I've talked quite a bit on here (and over on Panda's Thumb) about the importance of surveillance, and how the current death rates from H5N1 influenza ("bird flu") are likely to be artificially high, since we're more likely to diagnose the very ill cases than the mild or asymptomatic ones. (See here and here for the relevant posts). Indeed, that first post linked discusses a study carried out here at the Center for Emerging Infectious Diseases at the U of Iowa, which found that swine workers were much more likely to be infected with swine influenza viruses than those without significant swine contact--showing that there's likely a heckuva lot more sub-clinical or unrecognized cases of zoonotic influenza than ever pop up on the radar. A new study from Vietnam suggests the same thing, only surveying for "bird flu" and bird contact rather than swine. The abstract:

Background The verified human cases of highly pathogenic avian influenza in Vietnam may represent only a selection of the most severely ill patients. The study objective was to analyze the association between flulike illness, defined as cough and fever, and exposure to sick or dead poultry.

Methods A population-based study was performed from April 1 to June 30, 2004, in FilaBavi, a rural Vietnamese demographic surveillance site with confirmed outbreaks of highly pathogenic avian influenza among poultry. We included 45 478 randomly selected (cluster sampling) inhabitants. Household representatives were asked screening questions about exposure to poultry and flulike illness during the preceding months; individuals with a history of disease and/or exposure were interviewed in person.

Results A total of 8149 individuals (17.9%) reported flulike illness, 38 373 persons (84.4%) lived in households keeping poultry, and 11 755 (25.9%) resided in households reporting sick or dead poultry. A dose-response relationship between poultry exposure and flulike illness was noted: poultry in the household (odds ratio, 1.04; 95% confidence interval, 0.96-1.12), sick or dead poultry in the household but with no direct contact (odds ratio, 1.14; 95% confidence interval, 1.06-1.23), and direct contact with sick poultry (odds ratio, 1.73; 95% confidence interval, 1.58-1.89). The flulike illness attributed to direct contact with sick or dead poultry was estimated to be 650 to 750 cases.

Conclusions Our epidemiological data are consistent with transmission of mild, highly pathogenic avian influenza to humans and suggest that transmission could be more common than anticipated, though close contact seems required. Further microbiological studies are needed to validate these findings.

Though intriguing, there are some major weaknesses in the study. First, it's all self-reported, without any serological evidence, and "flu-like illness" ain't exactly definitive of actually having influenza. But it's certainly suggestive, and once again highlights what so many in public health have been trying to pound into the heads of those who control the funds: we need better surveillance, period.

Other scientists seem to be a bit more optimistic. According to this AP article:

"I would call this the smoking gun," said Dr. Gregory Poland, a Mayo Clinic flu specialist. "All of us have been concerned and have guessed that the data we have so far has been the tip of the iceberg."

The human cases counted so far likely have been the most severely ill patients treated at major hospitals, Poland said.

"In the really rural areas, we know that this had to be occurring" too, and the study suggests that the prevalence "is pretty high," he said. "The data lines up biologically the way we would have expected it to."

I agree with a lot of that, but wouldn't call this a "smoking gun" in any way, shape, or form. Maybe it would have been if they'd definitively shown H5N1 seroconversion before and after bird exposure, but the "influenza-like illness" category is just too broad. Even other bird diseases that humans can acquire, such as psittacosis, can cause influenza -like symptoms--so I think Dr. Poland is overshooting. Hopefully this will help to get other studies funded, though.

I've not been writing much on the recent developments with H5N1, so for anyone who's not up to speed, check out Effect Measure, where they've been keeping up much better on the newest influenza news. And while those of us who report on the science are generally a bit more clinical about the suffering, Revere also reminds us of the more personal side, noting that one family in Turkey has now lost a son and two daughters to H5N1--a second son, age 6, survives. This is why it's so much easier to deal with stats--numbers, even when contemplating a large amount of deaths, are less difficult than the personal story of just one victim.

Edited to add this news story:

Two young brothers, ages 4 and 5, who have tested positive for the dreaded H5N1 avian virus but shown no symptoms of the disease were being closely watched at Kecioren Hospital here Tuesday. Doctors are unsure whether they are for the first time seeing human bird flu in its earliest stages or if they are discovering that infection with the H5N1 virus does not always lead to illness.

In any case, the highly unusual cluster of five cases detected in Turkey's capital over the last three days -- all traceable to contact with sick birds -- is challenging some of the doctors' assumptions about bird flu and giving them new insights into how it spreads and causes disease. Since none of the five has died, it is raising the possibility that human bird flu is not as deadly as currently thought and that many mild cases in Asian countries may have gone unreported.