Influenza viral infections among the Iranian Hajj pilgrims returning to Shiraz, Fars province, Iran

BACKGROUND Annually over two million Muslims from across the world converge on Mecca to perform the Hajj pilgrimage. Overcrowding at the Hajj facilitates spread of communicable diseases, especially respiratory infections. The aim of this study was to determine the attack rate of seasonal and pandemic influenza among returning Iranian pilgrims after the 2009 Hajj. METHODS Clinical data and throat swabs were collected at Shiraz airport from symptomatic Iranian pilgrims of Fars province who were returning from the Hajj between 15 and 21 December 2009. The specimens were tested at the Shiraz University of Medical Sciences Influenza Research Center for influenza viruses by cell culture and real-time reverse transcriptase polymerase chain reaction (RTrtPCR) according to standard protocol. FINDINGS Out of 3000 pilgrims from Fars province who attended the Hajj 2009, 275 symptomatic pilgrims were recruited into this study. Pilgrims had fever, cough, muscle ache and sore throat in various combinations. Twenty-five (9.1%) pilgrims had influenza by virus culture and these were as follows: influenza B (n=17), influenza A H3N2 (n=8) and pandemic H1N1 (n=5), whereas 33 (12%) had influenza by RTrtPCR: influenza B (n=20), influenza A H3N2 (n=8) and pandemic H1N1 (n=5). INTERPRETATION Both seasonal and pandemic influenza infections occurred among the Iranian Hajj pilgrims; seasonal viruses were more common than the pandemic viruses even though all pilgrims were vaccinated against seasonal influenza.