Some observers were clearly shocked. Others predicted that it was only a matter of time before H5N1 reached out from poultry to touch the human race somewhere on the Indian sub-continent. Nevertheless, there was surprise at the size of the extended family cluster in Pakistan of infection with the H5N1 strain of highly pathogenic avian flu (HPAI). There was a further surprise: it had begun on 25 October 2007 but was only announced to the world on 9 December. Even then, first reports were so confusing that it took another week before the outside world realised the significance of events.

World Health Organization (WHO) has since added clarity to the situation. Pakistani authorities announced six persons in or close to one family infected with H5N1, although WHO says at least nine have tested positive for H5N1. It also said investigations are continuing to find out and confirm just how the various people in the cluster became infected, adding that some human-to-human transmission is possible. “We can't rule it out,” said WHO spokesperson, Gregory Hartl, speaking from Geneva. “There are other plausible explanations. We don't know enough at this point. And in some of these cases, one never will know enough,” he commented to Canadian press.

The cluster involves four brothers and two cousins living in the country's North West Frontier province. First infected was a man who had worked on a chicken farm in Maneshra where he culled sick birds thought to be infected with H5N1. All other cases in the cluster apparently had no direct contact with the chicken farm. Another brother died without having been tested.

A doctor who treated these patients subsequently tested positive for H5N1 although there is some doubt over the type of test used so the doctor will be tested again. Three people who are not relatives but were involved in culling H5N1-infected poultry in the same area have also tested positive, according to the WHO.

Another brother from the family returned to the USA after visiting the family in Pakistan. This has caused consternation in the United States. US health officials say they conducted H5N1 testing on a man who had recently visited Pakistan and was complaining of mild respiratory symptoms. A spokesperson for the US Centers for Disease Control (CDC) confirmed that specimens had been taken from the man but that tests showed he was not infected with the virus.

There is international concern about the length of time taken to identify, confirm and announce what is the first ever human case in Pakistan and a large cluster of  H5N1 cases.

Nevertheless, Gregory Hartl of WHO is quoted as saying, “We feel that the Pakistanis have done everything right in terms of their response. He noted that the country has done a huge amount of work to strengthen infection control and increase surveillance but added, “Yes, they could have alerted us earlier.”

Another controversy has arisen over the number of H5N1 cases. Pakistan has counted six cases with one fatality but this excludes the brother who died without being tested, and the doctor whose first result was positive.

In all fairness, Pakistan has made no effort to hide this human H5N1 cluster being irrevocably linked to infected poultry. Two recent H5N1 outbreaks in poultry in the same province are already logged with the World Organisation for Animal Health (OIE). These started on 23 October and 28 November and resulted in a total loss (through disease or by culling) of 58,500 broiler breeders.

This is in direct contrast to the recent clusters of human cases in Jiangsu province in China and a city near to Indonesia’s capital, Jakarta. In these cases, the local authorities disclaimed any knowledge of H5N1 in poultry in the area and commented that the victims ‘had no known contact with sick fowls’. This makes it difficult for experts trying to establish the exact route of virus transmission from poultry to people. Given the widespread ownership of backyard poultry in Indonesia and parts of China, and the endemic status of H5N1, it is doubtful whether anyone in affected regions has not been near an infected chicken, duck, goose or cat.

Establishing and admitting a connection between infection in poultry and human cases is vital for all countries – however embarrassing – to enable the world’s veterinarians, virologists and influenza experts to determine type and magnitude of risk and mode of H5N1 transmission within the overall relationship between birds and humans.