Academic journal article Bulletin of the World Health Organization

Performance of Case Definitions Used for Influenza Surveillance among Hospitalized Patients in a Rural Area of India/Resultats Des Definitions De Cas Utilisees Pour la Surveillance De la Grippe Chez Des Patients Hospitalises Dans Une Region Rurale De l'Inde/Consideracion De Las Definiciones De Casos Empleadas Para la Vigilancia De la Gripe Entre Los Pacientes Hospitalizados En Un Area Rural De India

Academic journal article Bulletin of the World Health Organization

Performance of Case Definitions Used for Influenza Surveillance among Hospitalized Patients in a Rural Area of India/Resultats Des Definitions De Cas Utilisees Pour la Surveillance De la Grippe Chez Des Patients Hospitalises Dans Une Region Rurale De l'Inde/Consideracion De Las Definiciones De Casos Empleadas Para la Vigilancia De la Gripe Entre Los Pacientes Hospitalizados En Un Area Rural De India

Article excerpt

Introduction

Case definitions for influenza surveillance need to be simple, easily understood and easily implemented. The international standardization of such case definitions is difficult, partly because the optimal choice of case definition depends on the population involved and the objectives of the surveillance. The World Health Organization (WHO) arranged a consultation on this topic in 2011 and is currently developing a document to describe minimum global standards for influenza surveillance case definitions. In the surveillance of severe influenza requiring hospitalization, the WHO currently recommends a particular case definition for severe acute respiratory illness: "cough or sore throat, plus measured fever, shortness of breath and need for hospitalization" (Table 1). In the surveillance of outpatient influenza, however, WHO recommends using the case definition for influenza-like illness (measured fever plus cough or sore throat). Despite this recommendation, in some countries a case definition for acute respiratory illness is used to evaluate outpatient influenza.

The case definitions used in national and regional influenza surveillance programmes often differ from those recommended by WHO. (1-8) However, most case definitions used for influenza surveillance include measured or reported fever as well as cough and/or sore throat. Some also include constitutional symptoms, such as joint pain, myalgia, headache and/or malaise. A case definition for febrile acute respiratory illness has been used in the detection of influenza in research settings. (9)

The performance of influenza case definitions has been evaluated many times but only among ambulatory or hospitalized patients with fever or respiratory symptoms. (10-20) Such evaluations may have missed influenza cases with atypical clinical presentations, particularly those caused by acute exacerbations of underlying disease. In the Hong Kong Special Administrative Region of China and in the United States of America, >75% of all cases of influenza-associated severe disease have been found to be classified not as influenza but under the underlying condition (e.g. cardiovascular disease, chronic lung disease or diabetes) that placed the individuals at risk. (21,22)

We conducted a study to estimate the burden of hospitalized influenza in a rural community in western India between 2009 and 2011. To maximize the detection of patients with hospitalized influenza, we screened all hospital admissions and enrolled patients with any acute medical illness of recent onset, including acute exacerbations of underlying chronic conditions. After using a reverse-transcription polymerase chain reaction (PCR) to identify patients infected with influenza virus, we retrospectively evaluated the sensitivity and specificity of various case definitions, including those that are commonly used for the detection of influenza among hospitalized patients.

Methods

Setting

The study area of Vadu lies in Pune district, 30 km to the northeast of Pune city, in western India. Vadu has a health-care infrastructure that is typical of a rural area in close proximity to a larger town or city in India. The public sector includes a rural hospital and primary health centres and the private sector includes several small general hospitals. Medical care is easily accessible. Most residents seek care in the private sector, which is largely unregulated. Hospital admission, treatment and pricing guidelines are often unclear, not standardized and subject to the providers' preferences. For the present study, surveillance for hospitalized influenza cases was conducted in 29 general public and private hospitals (with a mean of 15 beds per hospital) in and around the 22 villages of the Vadu Demographic Surveillance Area (DSA) in Pune district. In the study area, the monsoon and winter seasons run from June to September and November to February, respectively. …

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