Study shows high level of avian to human transmission of influenza A (H7N7) during outbreak in the Netherlands 2003 - NETHERLANDS - A report on the highly pathogenic avian influenza (HPAI) (H7N7) outbreak that occurred in the Netherlands in 2003 has been published.

Koopmans et al. describe the epidemiological and virological results of case finding during the outbreak period, and the preventative measures implemented (1). The outbreak began at the end of February 2003 and the Dutch Ministry of Agriculture announced a ban on the export of all poultry and poultry related products on 1 March. During the outbreak the infection spread to 225 farms, and led to the culling of approximately 30 million chickens.

Active case finding was implemented among poultry workers, poultry farmers and their families following an increase in anecdotal reports of health complaints from people involved in the control of the animal epidemic. Health complaints were reported among 453 people, with conjunctivitis the most commonly report symptom (349 cases). Influenza A (H7N7) was detected in 89 (19.6%) cases. There was one human fatality during the outbreak, a 57 year old veterinarian who had visited several farms with HPAI infected poultry flocks (2). In addition, three contacts of confirmed influenza A (H7N7) cases tested positive for influenza A/H7infection.

Control measures were implemented early during the outbreak. Following confirmation of influenza A (H7N7) as the cause of the avian influenza outbreak on 3 March, all workers in contact with poultry were advised to wear protective glasses and face masks. Shortly afterwards, and following the increase in cases of human infection, influenza vaccination was offered to, and accepted by, all poultry workers involved in handling, screening or culling potentially infected poultry. This policy was aimed at reducing possible genetic mixing or reassortment of avian and human influenza viruses in one infected person. The influenza vaccination recommendation was subsequently extended to all poultry workers and their families in a 3km radius of infected poultry farms, and those suspected of having the infection. Treatment with oseltamivir was recommended for all conjunctivitis cases, and a prophylactic regimen of oseltamivir was given to all people handling potentially infected poultry for two days after their last exposure.

Virological sequence data published elsewhere indicate that the virus strains were of entirely avian origin, with no human genes (3). The virus isolated from the fatal case had, however, accumulated significant mutations, which may have been associated with enhanced virulence in this case. Further cohort studies are also underway to compare infection rates between different categories of poultry workers, and examine the effects of various risk factors.

This study describes a large outbreak of avian influenza infection in humans, with possible person to person spread among household contacts. The authors highlight the difficulty of implementing control measures early in the outbreak, when few data were available on which to base their decisions. They note that by the time prophylactic measures were reinforced one week after confirmation of the first human infection, more than one thousand people within the Netherlands and from abroad had already been exposed to this avian influenza variant, thus demonstrating the need for pandemic preparedness.

References:
Koopmans M, Wilbrink B, Conyn M, Natrop G, van der Nat H, Vennema H et al. Transmission of H7N7 avian influenza A virus to human beings during a large outbreak in commercial poultry farms in the Netherlands. Lancet 2004; 363: 587-93.

Crofts J. Avian influenza human death reported in the Netherlands. Eurosurveillance Weekly 2003; 7(17): 24/04/2003. (http://www.eurosurveillance.org/ew/2003/030424.asp)

Fouchier R, Schneeerger P, Rozendaal F, Broekman J, Kemink S, Munster V et al. Avian influenza A virus (H7N7) associated with human conjunctivitis and a fatal case of acute respiratory distress syndrome. Proc Nat Acad Scien 2004; 101: 1356-1

Source: Nichola Goddard - Health Protection Agency - 27th February 2004