Researchers Evaluate Timeliness of Contact Tracing Among Flight Passengers for H1N1 Influenza

During the initial containment phase of influenza A/H1N1 2009, close contacts of cases were traced to provide antiviral prophylaxis within 48 hours after exposure and to alert them on signs of disease for early diagnosis and treatment. Passengers seated on the same row, two rows in front or behind a patient infectious for influenza, during a flight of [greater than or equal to] four hours were considered close contacts. Corien M. Swaan, of the Preparedness and Response Unit of the Centre for Infectious Disease Control, National Institute for Public Health and the Environment in the Netherlands, and colleagues, evaluated the timeliness of flight-contact tracing (CT) as performed following national and international CT requests addressed to the Center of Infectious Disease Control (CIb/RIVM), and implemented by the Municipal Health Services of Schiphol Airport.

Elapsed days between date of flight arrival and the date passenger lists became available (contact details identified - CI) was used as proxy for timeliness of CT. In a retrospective study, dates of flight arrival, onset of illness, laboratory diagnosis, CT request and identification of contacts details through passenger lists, following CT requests to the RIVM for flights landed at Schiphol Airport were collected and analyzed.

Twenty-four requests for CT were identified. Three of these were declined as over four days had elapsed since flight arrival. In 17 out of 21 requests, contact details were obtained within seven days after arrival (81 percent). The average delay between arrival and CI was 3.9 days (range 2-7), mainly caused by delay in diagnosis  of the index patient after arrival (2.6 days). In four flights (19 percent), contacts were not identified or only after >seven days. CI involving Dutch airlines was faster than non-Dutch airlines (P < 0,05). Passenger locator cards did not improve timeliness of CI. In only three flights contact details were identified within two days after arrival.

The researchers concluded that CT for influenza A/H1N1 2009 among flight passengers was not successful for timely provision of prophylaxis. CT had little additional value for alerting passengers for disease symptoms, as this information already was provided during and after the flight. Public health authorities should take into account patient delays in seeking medical advise and laboratory confirmation in relation to maximum time to provide post-exposure prophylaxis  when deciding to install contact tracing measures. International standardization of CT guidelines is recommended. Their research was published in BMC Infectious Diseases. 

Reference: Swaan CM, et al. Timeliness of contact tracing among flight passengers for influenza A/H1N1 2009. BMC Infectious Diseases 2011, 11:355. doi:10.1186/1471-2334-11-355