Infectious Disease
Severity of Respiratory Illness and Influenza-Associated Hospital Admissions in Kenya ― January–May 2023 Elizabeth White* Elizabeth White Nzisa Liku Bryan Nyawanda Victor Opere Jorim Ayugi Joel Machuki Peter Muturi Rosalia Kalani Nancy Otieno Danielle Iuliano Gideon Emukule
Introduction: Kenya has a high burden of respiratory illness and two seasonal influenza epidemics each year (January–March and June–August). Surveillance data are used to monitor influenza activity and guide resource allocation. We established intensity thresholds (ITs) to assess respiratory illness and influenza-associated hospitalization severity during January–May 2023.
Methods: We used the Moving Epidemic Method to calculate ITs for (1) the percentage of hospitalizations for severe respiratory illness (SRI), defined as admissions with a respiratory diagnosis (e.g., pneumonia) and (2) the percentage of hospitalizations attributable to influenza, obtained by multiplying indicator (1) by % influenza test positivity. Hospitalizations and diagnoses were abstracted from admission registers at five hospitals and summarized by week. Weekly influenza test positivity was from the same hospitals. ITs were calculated using 2019, 2021, and 2022 as baseline years, excluding 2020 due to the COVID-19 pandemic. Moderate, high, and very high ITs were defined as the 50th, 90th, and 98th percentiles, respectively, of the geometric mean and standard deviation of the 30 highest weekly values in baseline years (10 values per year). We compared weekly surveillance data from January–May 2023 with ITs to assess severity of each outcome during that period.
Results: During January–May 2023, % SRI reached a peak of 31.6%, below the IT50 (32.1%), indicating low severity. The percentage of hospital admissions for influenza reached a peak of 4.7%, above the IT50 (4.1%) but below the IT90 (6.3%), indicating moderate severity.
Conclusions: This is the first analysis of respiratory illness and influenza-associated hospitalization severity in Kenya. In early 2023, respiratory hospitalizations were low and influenza-associated hospitalizations were moderate compared to baseline years. ITs will be updated annually with additional baseline data, and severity can be assessed in future epidemic periods.
