Evaluation of an influenza-like illness case definition in the diagnosis of influenza among patients with acute febrile illness in cambodia

Passive clinic-based surveillance was established at nine healthcare centers to identify the causes of acute undifferentiated fever in patients aged two years and older seeking treatment. Fever was defined as tympanic membrane temperature >38°C lasting more than 24 hours and less than 10 days. Influenza virus infections were identified by polymerase chain reaction.From July 2008 to December 2008, 2,639 patients were enrolled. From 884 (33%) patients positive for influenza, 652 presented with ILI and 232 acute fever patients presented without ILI. Analysis by age group identified no significant differences between influenza positive patients from the two groups. Positive predictive values (PPVs) varied during the course of the influenza season and among age groups.The ILI case definition can be used to identify a significant percentage of patients with influenza infection during the influenza season in Cambodia, assisting healthcare providers in its diagnosis and treatment. However, testing samples based on the criteria of fever alone increased our case detection by 34%.Globally, influenza is considered one of the most important infectious diseases. It is reported that between 3 and 5 million cases of severe influenza disease occur each year [1], with estimated annual influenza-associated mortality between 500,000 and 1,000,000 cases (median case-fatality of 190 deaths per 100,000 person infected with influenza) [2,3]. Complicating the global influenza burden is the recent recognition of a novel quad-reassortment swine-origin influenza A virus which is the agent associated with the WHO declared influenza pandemic [4].Influenza viruses are transmitted through the respiratory route [5-8] and infections vary from asymptomatic to severe, life threatening. Common clinical symptoms of influenza include fever, cough, sore throat, headache, muscle aches, nasal congestion and weakness [9]. These symptoms can be non-specific and do not easily distinguish influenza from other r