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Outbreak of fowl plague (avian influenza) leads to secondary human cases, March 2003, the Netherlands

A. Meijer ¹, M. Du Ry van Beest Holle (mirna.dury@rivm.nl) ^{2, 3}, R. Fouchier ⁴, G. Natrop ⁵, B. Wilbrink ¹, A. Bosman ^2,3, A. Osterhaus ⁴, J. van Steenbergen ⁶, M. Conyn-van Spaendonck ², M. Koopmans ¹.

1 National Institute for Public Health and the Environment (RIVM), Diagnostic Laboratory for Infectious Diseases and Perinatal Screening
2 National Institute for Public Health and the Environment (RIVM), Centre for Infectious Disease Epidemiology
3 European Programme for Intervention Epidemiology Training (EPIET),
4 Erasmus Medical Centre Rotterdam, Department of Virology
5 Municipal Health Service
6 Office of the National Coordination Structure for Infectious Disease Control

The National Institute for Public Health and the Environment (RIVM) in the Netherlands, in collaboration with a multi organisation partnership, has implemented enhanced surveillance in response to the outbreak of highly pathogenic avian influenza (Influenza A/H7N7) in several Dutch poultry farms (1). The latest results (up to 19 March 2003) show that, among the population exposed to infected poultry, there have been 169 persons with acute health problems. Of the 132 persons with conjunctivitis, 29 also reported having ILI.

Of the 169 patients, 35 (20.7 %) tested positive for influenza A/H7N7, 5 were H3 positive, 25 were influenza negative, and in 104 patients, results were pending. Of 132 patients with conjunctivitis, 32 of 54 test results available were positive for H7N7 (59.3 %). Three patients with positive H7N7 results had unknown or other (no conjunctivitis or ILI) symptoms. So far no double infections with influenza A/H7N7 virus and H1 or H3 influenza viruses have been found.

In view of the unexpectedly high number of H7 associated eye infections, people exposed to infected poultry were asked to report clinical symptoms. Subsequently, conjunctival swabs and throat swabs were obtained and tested for the presence of viral RNA. Two contacts of a worker exposed to avian influenza infected poultry and suffering from conjunctivitis, developed similar symptoms. Both contacts were A/H7N7 positive. Neither contact had had direct exposure to the infected poultry. These results strongly suggest person to person transmission of A/H7N7 virus.

In order to prevent infection of persons exposed to avian influenza, all those involved in the control of infected poultry flocks have been provided with protective clothing, spectacles, and masks to cover the mouth and nose. The importance of hygiene measures such as hand washing has been emphasised. Approximately 1500 persons involved with the culling, as well as the families at the contaminated farms, are being vaccinated.

The findings from the enhanced surveillance, indicating person to person transmission, last week prompted the outbreak management team to recommend anti viral prophylaxis (oseltamivir) for all exposed persons. This advice from the State Secretary for Public Health, Ms. Ross, was implemented by the Municipal Health Services and local healthcare workers. Further, new cases will also receive anti viral treatment. The influenza A/H7N7 virus is susceptible to oseltamivir with a 50 % inhibitory concentration of 1.29 nM (95 % confidence interval 1.19-1.40 nM).

Routine human influenza virus surveillance shows that influenza (mostly A/H3N2) viral activity remains low in the Netherlands. Co-infection with both human and avian influenza virus could potentially lead to a reassortment of both viruses and result in a new pandemic. The circulation of both H7 and regular human influenza viruses within the same risk group is the reason for increased vigilance.