Review
Seasonal influenza epidemiology in sub-Saharan Africa: a systematic review

https://doi.org/10.1016/S1473-3099(11)70008-1Get rights and content

Summary

Acute respiratory infection (ARI) is a leading cause of mortality worldwide, of which influenza is an important cause that can be prevented with vaccination. We did a systematic review of research published from 1980 to 2009 on seasonal influenza epidemiology in sub-Saharan Africa to identify data strengths and weaknesses that might affect policy decisions, to assess the state of knowledge on influenza disease burden, and to ascertain unique features of influenza epidemiology in the region. We assessed 1203 papers, reviewed 104, and included 49 articles. 1–25% of outpatient ARI visits were caused by influenza (11 studies; mean 9·5%; median 10%), whereas 0·6–15·6% of children admitted to hospital for ARI had influenza identified (15 studies; mean 6·6%; median 6·3%). Influenza was highly seasonal in southern Africa. Other data were often absent, particularly direct measurement of influenza incidence rates for all ages, within different patient settings (outpatient, inpatient, community), and for all countries. Data from sub-Saharan Africa are insufficient to allow most countries to prioritise strategies for influenza prevention and control. Key data gaps include incidence and case-fatality ratios for all ages, the contribution of influenza towards admission of adults to hospital for ARI, representative seasonality data, economic burden, and the interaction of influenza with prevalent disorders in Africa, such as malaria, HIV, and malnutrition.

Introduction

Pneumonia is the leading cause of paediatric mortality worldwide1, 2 and infections such as Streptococcus pneumoniae, Haemophilus influenzae type b, and respiratory syncytial virus are well recognised contributors to global disease burden.3, 4, 5, 6, 7 Recent studies have documented the substantial role of influenza in respiratory infection morbidity and mortality at all ages,8, 9, 10, 11, 12, 13, 14, 15, 16, 17 although results from other studies have cast doubt on some of the reports from elderly patients.18, 19 Modelling analyses have estimated yearly excess mortality attributable to influenza in the USA to be about 30 000 between 1976 and 2007, depending on the year and underlying assigned cause.16 Other studies have documented the effect of influenza on work11, 20 and school absenteeism11, 21, 22 and on the economic costs of influenza.23, 24, 25, 26, 27 Influenza also contributes to acute respiratory infection (ARI) burden by increasing the risk of bacterial pneumonia, particularly that caused by pneumococci.28, 29, 30, 31

About 1·1 billion people live in sub-Saharan Africa, an area that has high population growth rates, low life expectancy, and many of the world's poorest countries.32 Despite the abundance of information from many areas of the world, little is known about influenza epidemiology in sub-Saharan Africa,33 and no systematic review has been published. We aimed to help identify data gaps that might affect policy decisions (such as routine vaccine use and target groups and the need for antiviral drugs), to assess the state of knowledge on seasonal influenza epidemiology in sub-Saharan Africa, and to ascertain unique features of influenza epidemiology in the region. We concentrated on sub-Saharan Africa because epidemiological, socioeconomic, and vaccine policy factors in northern Africa are likely to be substantially different. We focused on seasonal human influenza because data on pandemic or avian and animal influenza are unlikely to greatly inform routine yearly influenza prevention and treatment decisions.

Section snippets

Search strategy and selection criteria

We searched the National Library of Medicine through PubMed for (“influenza” AND “Africa”) OR (“Africa” AND (“pneumonia” OR “acute respiratory infection”)) OR (“influenza” AND each individual sub-Saharan African country); sub-Saharan African countries were defined by the UN Educational, Scientific and Cultural Organization34 with the addition of Reunion. The search was limited to studies of people, studies published in English, French, or Portuguese, and studies published from Jan 1, 1980, to

Results

We screened the titles and abstracts of 1203 published articles (figure 1). 49 are included in this report.42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90

Studies varied substantially on the basis of the number of years of assessment, age-groups included, number of influenza isolates obtained, testing methods implemented, and clinical case definitions

Discussion

As documented in a brief review published in 2002,93 little influenza surveillance infrastructure existed at that time in sub-Saharan Africa. Between 2002 and 2007, of the 46 WHO African Region countries, only South Africa, Senegal, and Madagascar routinely reported influenza activity to WHO, with sporadic reporting from Zambia, Uganda, Mauritius, Reunion, and Kenya.35, 36, 37, 38, 39, 40, 41 We found few published influenza epidemiology data in sub-Saharan Africa, which were concentrated in

Search strategy and selection criteria

These are described in detail in the Methods section.

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