People exposed to chickens on Dutch poultry farms affected by H7N7 avian influenza A virus (A/H7) were asked to report signs of conjunctivitis or influenza-like illness from February to June 2003. Of the estimated 3410 or more at risk, 453 had health complaints: 349 conjunctivitis; 90 influenza-like illness, and 67 others. Laboratory confirmation from eye and nose/throat swabs was by RT-PCR or viral culture and typing. A/H7 was detected in 83 (23.8%) patients with conjunctivitis, seven (7.8%) with influenza-like illness, and four (6.0%) with other symptoms. Influenza-like symptoms were reported less often in those who were A/H7 positive than in those in whom viruses could not be detected. There was one case fatality from respiratory distress syndrome and A/H7 was detected by bronchoalveolar lavage. After 19 people were diagnosed, all workers received influenza virus vaccination and prophylaxis with oseltamivir to reduce the risk of genetic mixing or reassortment of avian and human influenza virus.

This study shows an unexpectedly high number of A/H7 transmissions to humans. The virus is highly lethal in chickens but has comparatively low pathogenicity in humans. However, a more virulent virus would have been difficult to contain with current strategies and the study demonstrates the importance of surveillance and planning for possible future outbreaks.