Epidemiological aspects of pandemic influenza A(H1N1) virus from 2009 to 2011 in Iran

To the editor: As the world was preparing for a pandemic influenza of avian origin, in April 2009 a novel influenza A virus H1N1 strain of swine origin, now known as pandemic A(H1N1) 2009 virus (abbreviated as pH1N1), emerged in Mexico and spread quickly worldwide. On April 24, 2009, the World Health Organization announced a Public Health Emergency of International Concern caused by this new influenza virus variant. Approximately 8 weeks later on June 20, 2009, the first case of pH1N1 in Iran was reported in a traveler from the United States. Following the detection of the first imported confirmed pH1N1 infection in Iran, the National Influenza Center in collaboration with the Ministry of Health enhanced surveillance for pH1N1 virus infection in addition to the existing sentinel surveillance system for seasonal influenza and imposed entry screening on travelers from affected areas. Specimens were collected for laboratory testing from suspected cases with influenza-like illness (ILI) symptoms, fever with history of recent traveling, or having a contact with a confirmed case of pH1N1. The population of Iran is around 75 million. This letter reports the available epidemiological characteristics of 40 169 suspected cases of pH1N1 infection between June 20, 2009 and November 21, 2011. During July through September 2009, Iran experienced some transmission of pH1N1; a stronger wave began in October, and a peak occurred in November and then declined steadily. There was a small second wave in early 2011. Among the total of 40 169 suspected cases, 5214 (12Æ9%) were confirmed cases with real-time RT-PCR (using the Invitrogen SuperScript III Platinum with specific primers obtained from the United States Centers for Disease Control and Prevention real time RT-PCR Protocol) of whom 230 (4Æ4%) were classified as imported, travel-associated cases. As shown in Figure 1, the highest incidence of confirmed cases occurred in October and November 2009, after schools had reopened in September. School children are known to be important in transmission of influenza. During this outbreak, an increase in the number of absenteeism owing to ILI symptoms led schools to close in some parts of the country especially in the central and south-east regions of Iran.