10 May 2012
Influenza-associated burden of disease in low and middle income countries – Examples from Kenya, Bangladesh and China
In the April 2012 issue of the Bulletin of the World Health Organization – a special issue dedicated to influenza – the morbidity and/or mortality associated with influenza in middle and low-income country settings was assessed in three original research papers. In the first study, Feikin and colleagues (1) carried out a prospective surveillance study to estimate the burden and age-specific rates of influenza-associated hospitalization in Kenya. The study was carried out over a period of two years in one of the districts in the rural western part of the country, where swabs were collected from 2079 patients hospitalised with respiratory illness and tested for influenza viruses using RT-PCR. Of those specimens, 10% were positive and influenza A was predominant in the region, making up 86% of positive specimens. The rate of influenza-associated hospitalisation was found to be 56.2 per 100,000 population and it was highest among children aged less than five years of age. In the second paper, influenza-associated mortality in Bangladesh was assessed by Homaira and colleagues (2) using a combination of hospital-based surveillance and community surveys. Respiratory samples were collected from four hospitals in Bangladesh and tested for influenza using RT-PCR to measure the number of influenza-positive cases. Mortality data for the catchment area of each hospital was gathered through informal discussion groups and interviews with proxy respondents to identify patients who had died within 14 days of developing fever with cough and/or a sore throat in that year, and these deaths were assumed to be influenza-associated. Using these data and information from the 2001 census to estimate the total population, researchers found that the estimated mean annual influenza-associated mortality was 11 per 100,000 population, with the biggest burden seen among the elderly (125 deaths per 100,000). In the third study, Feng and colleagues (3) calculated influenza-associated excess mortality in China by applying negative binomial regression models to influenza virological surveillance data and mortality data for deaths for all causes and for deaths attributable to pneumonia and influenza between 2003 and 2008. Eight Chinese cities were included in the study – three in temperate northern China and five in tropical southern China – so as to represent the two influenza transmission zones in the country. The group calculated that the mean annual numbers of influenza-associated all-cause excess deaths in the northern and southern cities were 1825 and 2446, corresponded to 18 and 11.3 deaths per 100,000 population, respectively. Most influenza-associated excess deaths occurred among individuals aged 65 and over. The group also found that most influenza-associated mortality were associated with B viruses, followed by A(H3N2) viruses, whereas only 11% of these deaths in the northern and no deaths in the southern cities were associated with A(H1N1).
The global burden of influenza has been estimated to be 500,000 to 1 million deaths annually (4); however, information on the burden of influenza in middle and low-income countries is still very limited (5, 6). The three studies summarised above aimed to bridge this knowledge gap by measuring either morbidity or mortality associated with influenza in different developing countries. Previous studies have shown that influenza-associated mortality rates are higher in low-income than in high-income countries (7). The reasons for this are unknown, but are likely related to lack of access to adequate medical care, limited public health infrastructures, social factors such as health-seeking behaviour, housing conditions and population density, or host factors, such as underlying risk factors and medical conditions (8, 9). Although the results obtained in these three studies are not directly comparable due to the different methods used, they highlight some of the issues encountered when attempting to estimate influenza burden in these settings. A major issue in developing countries is the absence of suitable sentinel surveillance systems for influenza and the subsequent lack of year-round epidemiological and virological data for influenza-associated disease. Although these systems have theoretically been implemented in many developing countries, the limited health infrastructure and lack of trained staff has posed a problem for its implementation and regular use (9). Another issue encountered in these studies was the lack of a national system for the registration of vital statistics, such birth and mortality data (2, 3), which greatly hinders the assessment of influenza-associated morbidity and mortality. The WHO will soon be publishing a new document on Global Surveillance Standards for Influenza, which aims to standardise the case definitions for influenza-like illness (ILI) and severe acute respiratory illness (SARI) and highlights the importance of establishing a sentinel surveillance system for influenza monitoring over time, and where the sharing of influenza epidemiological and virological data is encouraged through web-based tools such as FluNet (10) and FluID (11). The implementation of this set of WHO standards in middle- and low-income country settings will increase our knowledge of influenza-burden in these settings, such as seasonality and circulating influenza strains, and would guide policy making with regards to the use of pharmaceutical interventions, such as antiviral agents and immunisation programmes. The adequate use of such interventions could help lower the burden posed by influenza virus in these settings.
(1)Feikin D.R., Ope M.O., et al. The population-based burden of influenza-associated hospitalization in rural western Kenya, 2007-2009. Bull. World Health Organ. 2012;90:256-263A
(2) Homaira N., Luby S.P., et al. Influenza-associated mortality in 2009 in four sentinel sites in Bangladesh. Bull. World Health Organ. 2012;90:272-278
(3) Feng L., Shay D.K., et al. Influenza-associated mortality in temperate and subtropical Chinese cities, 2003-2008. World Health Organ. 2012;90:279-288B
(4) Pan American Health Organization [PAHO]. Final report of the XVI Meeting on Vaccine Preventable-Diseases of the Pan American Health Organization. Washington (District of Columbia): PAHO; 2004. Available: http://www.paho.org/English/AD/FCH/IM/TAG16_FinalReport_2004.pdf.
(5) Charu V., Chowell G., et al. Mortality burden of the A/H1N1 pandemic in Mexico: a comparison of deaths and years of life lost to seasonal influenza. Clin Infect Dis.; 53:985-91
(6) Cohen C., Simonsen L., et al. Elevated influenza-excess related mortality in South African elderly individuals, 1998-2005. Clin Infect Dis. 2010; 51:1362-9
(7) Murray CJ, Lopez AD, et al. Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918–20 pandemic: a quantitative analysis. Lancet 2007;368:2211–8.
(8) Viboud C., Alonso W.J., and Simonsen L. Influenza in tropical regions. PLoS Med 2006; 3(4):e89
(9) Oshitani H., Kamigaki T., and Suzuki A. Major issues and challenges of influenza pandemic preparedness in developing countries. Emerg Infect Dis 2008; 14(6):875-80
(10) Flunet. http://www.who.int/influenza/gisrs_laboratory/flunet/en/
(11) FluID. https://extranet.who.int/fluid/