Using a hospital admission survey to estimate the burden of influenza‐associated severe acute respiratory infection in one province of Cambodia—methods used and lessons learned

Abstract

BackgroundUnderstanding the burden of influenza‐associated severe acute respiratory infection (SARI) is important for setting national influenza surveillance and vaccine priorities. Estimating influenza‐associated SARI rates requires hospital‐based surveillance data and a population‐based denominator, which can be challenging to determine.ObjectivesWe present an application of the World Health Organization's recently developed manual (WHO Manual) including hospital admission survey (HAS) methods for estimating the burden of influenza‐associated SARI, with lessons learned to help others calculate similar estimates.MethodsUsing an existing SARI surveillance platform in Cambodia, we counted influenza‐associated SARI cases during 2015 at one sentinel surveillance site in Svay Rieng Province. We applied WHO Manual‐derived methods to count respiratory hospitalizations at all hospitals within the catchment area, where 95% of the sentinel site case‐patients resided. We used HAS methods to adjust the district‐level population denominator for the sentinel site and calculated the incidence rate of influenza‐associated SARI by dividing the number of influenza‐positive SARI infections by the adjusted population denominator and multiplying by 100 000. We extrapolated the rate to the provincial population to derive a case count for 2015. We evaluated data sources, detailed steps of implementation, and identified lessons learned.ResultsWe estimated an adjusted influenza‐associated 2015 SARI rate of 13.5/100 000 persons for the catchment area of Svay Rieng Hospital and 77 influenza‐associated SARI cases in Svay Rieng Province after extrapolation.ConclusionsMethods detailed in the WHO Manual and operationalized successfully in Cambodia can be used in other settings to estimate rates of influenza‐associated SARI.

National burden of influenza-associated hospitalizations in Cambodia, 2015 and 2016

“…The Svay Rieng HR slightly differs from previously published rates ( 15 ) due to a different population data source used for their calculation.…”

“…50 SARI cases were reported by the surveillance system compared to 41 identified by medical records review). ( 15 )…”

“…( 15 , 16 ) First, the addresses of the SARI cases admitted to the sentinel site were reviewed, and the catchment area for each site was defined as the districts from which 80% of the SARI cases admitted to the sentinel hospitals came ( Fig. 1 ).…”

Human influenza viruses in South-East and East Asia: a systematic review of seasonal patterns, viral types/subtypes, and antiviral susceptibility pattern in the past two decades

“…Ever since the first influenza pandemic was reported in the 1580s, two of the three recent pandemics including the 1918 Spanish flu have originated from Asia which houses 60% of the world's population. 1,3,4,12,[14][15][16] The most recent pandemic caused by the novel influenza A virus strain A(H1N1) pdm09 which started in 2009 originated from Mexico and America and later spread to over 214 countries including South-East and East Asia causing over 18,449 deaths globally. 1,3,4,16,17 Surveillance data has shown influenza rates of 11-26% in out-patient and 6-14% in hospitalized patients in both regions.…”

“…9 Susceptible individuals include the very young, the elderly, immunocompromised individuals, pregnant women, and individuals with predisposing medical conditions such as renal and cardiac impairment. 1,4,12 Additionally, the virus has a diameter of approximately 120 nanometers and has an enveloped segmented RNA genome with antigenic molecules in their nucleocapsid. 1,2 Antigenic variations usually occur in both the A and B virus with the C virus being more antigenically stable.…”