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H5N1 Bird Flu Cluster in West Sumatra
September 15, 2006
The second case is a 27-year-old male from Solok, West Sumatra Province. This case was identified during the tracing of contacts of the man’s sister, a 15-year-old female who developed symptoms on 17 May 2006 and was subsequently confirmed to be H5N1 infected. Her brother spent six days caring for her during her hospital stay. The brother developed mild symptoms of cough and abdominal discomfort, with no fever, on 28 May 2006; his symptoms remained mild and he recovered within a few days.
Despite his mild and atypical symptoms, the brother was tested as part of the Ministry of Health’s protocol for contact tracing and the management of any contacts with symptoms. He was given a five-day course of oseltamivir beginning on 1 June and was placed in voluntary isolation pending recovery.
Initial tests of samples collected from the 27-year-old male were negative for H5N1 infection. In August, follow-up testing of paired-serum samples found a fourfold rise in neutralization antibody titer for H5N1,
The investigation determined that he had exposure to his sister during her hospital stay, and that human-to-human transmission could not be ruled out as the source of his infection.
The above comments in the latest WHO update describe a familial cluster in West Sumatra. The cluster follows the typical pattern of disease onset dates which include gap between the index case and other family members. Although most WHO updates discount human-to-human transmission because there are sick or dying birds linked in some way to the cluster, this report acknowledges the possibility of such transfer because there are few or no such links for the family member.
However, recent details on H5N1 in Vietnam provide additional evidence supporting frequent human-to-human transmission within families. The patients in Vietnam had levels of H5N1 in their noses that were similar to levels of seasonal flu in patients infected with human serotypes. Moreover, the H5N1 patients had significantly higher levels in their throats, and the patients with higher viral loads also had detectable H5N1 in blood and rectal samples.
This systemic spillage of H5N1 offered many opportunities for infection of family members because of contact with H5n1 from body fluids or contamination by sneezing or coughing. Over time, these transmission opportunities lead to frequent infection of family members in contrast to transmission from poultry, which is rare.
The above cluster also raises concerns over undetected H5N1 in mild cases. The family member described above initially tested negative for H5N1. His infection was confirmed because a paired serum sample was tested and the level of neutralizing H5N1 antibodies was four fold higher than an earlier sample.
The requirement for tests on two paired serum samples limits the number of confirmed cases because in many cases no sample is collected, and in another cases oly one sample is collected. Recent results from test on poultry workers in South Korea and Japan identify neutralizing H5N1 antibodies. These data suggest that the number of mild H5N1 infections in contacts and patients without links to dead or dying poultry is significantly hiher than the cases acknowledged by the WHO.
Neutralizing influenza antibodies in serum can be detected decades after exposure. Testing of surviving contacts of H5N1 patients is relatively straightforward as is testing of suspect patients.
Such testing of patients in Turkey and Indonesia are long overdue.