Trend of burden of influenza associated sari and factors associated with Sari in Kibondo District, Kigoma Region, Tanzania

Abstract

Background: Data on the burden of influenza in developing countries are limited. Despite the availability of influenza surveillance system in Tanzania, there is scarcity of information on the burden of influenza and its associated factors within the country. Thus this report present the results from a study aimed to assess the trend of influenza associated with severe acute respiratory infections (SARI) and their associated factors. Methods: We conducted a study with two components, a retrospective longitudinal study component and an unmatched hospital based case-control component in Kibondo district. The retrospective cohort study was conducted to determine the trend of influenza associated severe acute respiratory infection (SARI) using data the SARI patients records admitted during 2013 to 2015 registered in the influenza surveillance registers, data base of laboratory results for influenza among SARI from the Ministry of Health and other relevant hospital records. We used WHO manual for estimation and calculation of burden of influenza, data was collected by using formatted checklists. An unmatched hospital based case- control component was then conducted during March and April 2017 to determine factors associated with severe acute respiratory infections. Data were collected using a structured and pretested questionnaire among cases and controls at a ratio of 1:2. Data were analyzed by using Epi info version 3.5.1 and Stata software for descriptive statistics and unconditioned logistic regression at p < 0.05. Graphical work was done using Ms excel. Results: During 2013-2015, a total of 2705 SARI cases across all age groups were admitted at Kibondo sentinel hospital, out of those 2515(92.9%) cases were residents of Kibondo District council. A total of 1002 (39.8%) cases from whom clinical specimens were taken and180 (17.9%) were positive for influenza. Most of cases were children < 5 years (65.2%). The median age was 2 years, range (0.08 -90) years. The overall estimated incidence of influenza associated SARI during 2013-2015 was 317(95%CI: 274-368) per 100,000 persons-years. The estimated annual incidence of influenza associated SARI in 2013, 2014 and 2015, was 80 (95%CI: 62-104), 155(95% CI: 128-190) and 52 (95%CI: 33-82) per 100,000 persons-years respectively. The estimated incidence of influenza associated SARI in children < 5 years old was 277(95%CI 313-360); 574 (95%CI 479-689) and 136(95%CI 85-218) per 100,000 persons-years, during 2013, 2014 and 2015 respectively. The incidence of influenza associated SARI in people aged ≥ 5 years was 24(95%CI 14-44); 41(95%CI 25-70) and 24 (95%CI 8-75) per 100,000 person-years during 2013, 2014 and 2015 respectively. The annual hospital case fatality ratio in 2013, 2014, and 2015 was 0.9%, 1.6% and 2.9% respectively. There were higher hospital case fatality ratio among persons with age group of ≥ 5 years in 2013 and 2014 which was 4.2% and 2.9% respectively compared to children < 5years which was 2.1 and 1.1, respectively. The annual hospital case fatality ratio among < 5 years increased in 2015 which was 1.4 for < 5 years compared to ≥ 5 years which was zero. Annual influenza positivity among SARI cases in 2013, 2014 and 2015 were 8.8%, 47.4% and 17.4% respectively. Factors associated with severe acute respiratory infections (SARI) were passive smoking [OR 25.05(95%CI: 7.48-96.02)], indoor air pollution [OR 2.61 (95%CI: 1.10-6.19)] and contact with person with respiratory infections in the past seven days [OR 73.00 (95%CI: 18.82-283.16)]. Persons at the age group of < 5years were at higher risk for SARI compared to those at the age group of (25-44) [OR 18.93 (95%CI: 4.66-76.86)], also persons at the age group of ≥ 45 years were at higher risk for SARI compared to those at the age group of (25-44) [OR 5.46 (95%CI: 1.06-28.13)] respectively. Conclusions: We found substantive influenza burden leading to hospitalization and mortality in Kibondo district. Children aged < 5 years were hospitalized for influenza at higher rates than people aged ≥ 5 years. The hospital case fatality ratio was higher among persons ≥ 5 years compared to children < 5 years. Factors associated with SARI include; indoor air pollution, passive smoking, contacts a person with history of respiratory infections and age. The findings highlight the need for a wider study to explore the burden of influenza and reviews of SARI case management practices to provide adequate data for planning national wide management and preventive programmes. Furthermore, future studies should examine other causes of SARI apart from influenza virus and burden of influenza into key potential risk groups.