Limited novel influenza A (H1N1) 09 infection in travelling high-school tour group

A single case of novel influenza A (H1N1) 09 infection was identified by PCR among a New Zealand high-school group that toured California in April 2009. Close monitoring of the tour group and their New Zealand contacts identified 11 other tour members with respiratory symptoms who were investigated. In all nine instances where nasopharyngeal swabs were indicated, tests were negative for novel influenza A (H1N1) 09 by PCR.

To determine whether serology could identify any cases of novel influenza A (H1N1) 09 that had not been detected by PCR.

Acute and convalescent serological testing for antibodies against pandemic (H1N1) 2009 and seasonal A (H1N1) influenza viruses using haemagglutination inhibition assays and microneutralisation assays.

Serological analysis of symptomatic tour members identified a further possible case of novel influenza A (H1N1) 09 infection. The possible case had not been tested by PCR because he or she had already received prophylaxis with oseltamivir.

These findings suggest infection among tour group members was limited despite prolonged periods of close contact during travel. Furthermore, multiple public health interventions are likely to have effectively prevented an outbreak following the tour group's return.