# 302
While events are unfolding in Indonesia this seems like a good time to review some of the terms and criteria used in describing suspected cases of bird flu.
The assumption is that nearly all cases of human infection are due to B2H (Bird to Human) transmission of the virus. Someone handles, or consumes a stricken bird, and becomes infected. In most cases, the chain of transmission stops there.
While there have been cases where there was no documented contact with sick or dead poultry, for the most part, authorities look for some connection with domestic or wild birds before assuming anyone presenting with a fever/cough combination to be suspected of having the bird flu virus.
Most of the time, this assumption probably works pretty well.
Most human infections to date probably have been the result of direct contact with infected birds. This policy does open the door to missing, or dismissing potential bird flu cases, when no sick birds have been detected. Given that the vaccines in use may be producing asymptomatic birds capable of shedding the virus, at some point this criterion may prove to be a real problem.
The other side of this coin is that in countries like Indonesia, nearly all residents have some contact with birds or poultry. Most families raise a few birds in their backyards. This can lead to the false assumption that if someone is stricken with the virus, they must have acquired it from a bird.
Whenever a suspected case of bird flu is hospitalized, we are immediately informed that they had eaten, slaughtered, or buried a bird sometime in the past week or so. These accounts are sometimes vague, and the connections often tenuous. But the blaming of the `usual suspects’ is nearly always publicly announced, often before any other details are known.
While there has been speculation over other possible vectors, little work has been done in this area. Dogs, cats, pigs and other mammals have been suggested as potential carriers of the disease. Until some definitive link to one or more of these animals is detected, it is unlikely that they will be regarded seriously by the authorities as potential vectors of the virus.
A `Cluster’ can most easily be defined as `two or more cases linked by a common source or chain of infection’. If the same bird infects two people, then they would be considered a cluster. If two members of the same family contract the virus, even if we don’t know the exact route of infection, they can be assumed to be a cluster.
In the case of Riyah, and her son, both have tested positive, and so they make up a cluster. Riyah’s husband is also ill, and it is disputed in the media as to whether he has tested positive. No matter. Two in the same family is a cluster.
H2H (Human to Human) transmission is, to date, more rare. We've seen several clusters where it is strongly suspected. The concern is the virus will acquire the ability to efficiently transmit itself between humans, and thus set off a pandemic. That is why we watch clusters so carefully, watching for the first sign that the virus has mutated, and has gained this ability.
`Suspected’ cases are generally those that present with bird-flu like symptoms, and who have been exposed either to sick birds, or other suspected or confirmed bird flu cases. Pending a positive test result, these cases remain `suspected’, not confirmed.
The symptoms for H5N1 infection are very similar to any severe influenza or pneumonia at first, and so it is impossible to base a diagnosis on clinical findings alone. The tests for the H5N1 virus are notoriously inefficient at picking up the virus, however, and often must be repeated several times. Therefore it is possible that `suspected’ cases might either recover, or die, and never make it into the `confirmed’ category.
The administration of Tamiflu, generally the first therapeutic step taken when addressing a suspected H5N1 infection, can further complicate the testing.
While it is likely we have missed some H5N1 cases along the way, we have no idea how often that happens.
We are hampered by our limited knowledge of this virus. There is much we still don’t know, and much of what we think we know, may turn out to be wrong.
While I share the frustrations that many feel regarding the seemingly slow reaction to outbreaks in places like Indonesia, I also understand the limitations they have in dealing with a largely unknown pathogen in a developing country. There are economic, social, and cultural barriers that to those of us in the west, may seem difficult to comprehend.
We live in an imperfect world, with limited resources, and finite knowledge. Like it or not, we have to expect an imperfect response, even when the threat is that of a potential pandemic.
