Estimation of the national disease burden of influenza-associated severe acute respiratory illness in Kenya and Guatemala: a novel methodology

Abstract

Background: Knowing the national disease burden of severe influenza in low-income countries can inform policy decisions around influenza treatment and prevention. We present a novel methodology using locally generated data for estimating this burden.

Methods and findings: This method begins with calculating the hospitalized severe acute respiratory illness (SARI) incidence for children <5 years old and persons ≥5 years old from population-based surveillance in one province. This base rate of SARI is then adjusted for each province based on the prevalence of risk factors and healthcare-seeking behavior. The percentage of SARI with influenza virus detected is determined from provincial-level sentinel surveillance and applied to the adjusted provincial rates of hospitalized SARI. Healthcare-seeking data from healthcare utilization surveys is used to estimate non-hospitalized influenza-associated SARI. Rates of hospitalized and non-hospitalized influenza-associated SARI are applied to census data to calculate the national number of cases. The method was field-tested in Kenya, and validated in Guatemala, using data from August 2009-July 2011. In Kenya (2009 population 38.6 million persons), the annual number of hospitalized influenza-associated SARI cases ranged from 17,129-27,659 for children <5 years old (2.9-4.7 per 1,000 persons) and 6,882-7,836 for persons ≥5 years old (0.21-0.24 per 1,000 persons), depending on year and base rate used. In Guatemala (2011 population 14.7 million persons), the annual number of hospitalized cases of influenza-associated pneumonia ranged from 1,065-2,259 (0.5-1.0 per 1,000 persons) among children <5 years old and 779-2,252 cases (0.1-0.2 per 1,000 persons) for persons ≥5 years old, depending on year and base rate used. In both countries, the number of non-hospitalized influenza-associated cases was several-fold higher than the hospitalized cases.

Conclusions: Influenza virus was associated with a substantial amount of severe disease in Kenya and Guatemala. This method can be performed in most low and lower-middle income countries.

Figure 1. Overview of methodology for calculation of annual number of cases of influenza-associated Severe Acute Respiratory Illness (SARI) in a country.

Data input steps are in white boxes and data output are in shaded boxes.

Figure 2. Percentage of severe acute respiratory infections (SARI) that tested positive for influenza by Guatemalan department and Kenyan province.

August 2009-July 2011. Panel A-Children <5 years old. Panel B- Persons ≥5 years old.