8 October 2008
Pakistan 2007: Family cluster of 5 brothers with H5N1 Avian Flu infection includes the full clinical spectrum from fatalities to the (rare) asymptomatic household contact case
This week's "Weekly Epidemiological Record" of the World Health Organization provides a detailed description of the investigation of a family cluster in Pakistan last October-November (2007) of H5N1 avian influenza infection (www.who.int/wer 3 October 2008; No. 40. p 359-364). Several of the salient features of this cluster include:
1. The index case was most likely infected during culling of H5N1-infected poultry (without PPE) in the "poultry-belt" of the North-West Frontier Province (NWFP) of Pakistan. He developed a fever on October 29, 2007. On 2 November he travelled by public transport the four hours to his family's home in Peshawar, where 5 brothers and 2 sisters lived. WHO stated that he is "the first person to have documented influenza A (H5N1) disease following occupational exposure during poultry culling" (p. 363).
2. Four of his brothers (Cases 2-5) became ill with probable or lab-confirmed H5N1 infection. These cases included a 33 year-old brother who was asymptomatic, but had an H5-PCR+ throat swab and a positive H5 antibody test. This is a rarely-documented event, and the WHO report did not cite a single other example of asymptomatic seroconversion in household contacts of H5N1 patients, except during the 1997 Hong Kong H5N1 initial outbreak (J Infect Dis 1999; 180:1763-1770).
3. None of the four brothers had exposure to poultry. All had prolonged close contact with the index case and/or one another. Based on contact exposures between the brothers, and estimated incubation periods, the multiple investigator teams determined that human-to-human transmission occurred for "3 generations of transmission", but it was "not sustained in the community" beyond this one family (p. 364).
4. The full clinical spectrum was seen in Cases 1-5, including:
a.. Fatal infection: Case 2 and Case 3.
b. Recovery with intensive care (ICU) (for 9 days). Case 1 (index)
c. Recovery without intensive care: Case 4
(Oseltamivir ("Tamiflu" was begun one day after fever started).
d. Asymptomatic lab-confirmed infection.
Daniel R. Lucey, MD, MPH
EROne Institutes, Washington Hospital Center
Adjunct Professor of Microbiology and Immunology
Georgetown University Medical Center
website for this posting: www.BePast.org