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Epidemiology and etiology of childhood pneumonia Igor Rudan,a Cynthia Boschi-Pinto,b Zrinka Biloglav,c Kim Mulholland d & Harry Campbell e Abstract Childhood pneumonia is the leading single cause of mortality in children aged less than 5 years. The incidence in this age group is estimated to be 0.29 episodes per child-year in developing and 0.05 episodes per child-year in developed countries. This translates into about 156 million new episodes each year worldwide, of which 151 million episodes are in the developing world. Most cases occur in India (43 million), China (21 million) and Pakistan (10 million), with additional high numbers in Bangladesh, Indonesia and Nigeria (6 million each). Of all community cases, 7–13% are severe enough to be life-threatening and require hospitalization. Substantial evidence revealed that the leading risk factors contributing to pneumonia incidence are lack of exclusive breastfeeding, undernutrition, indoor air pollution, low birth weight, crowding and lack of measles immunization. Pneumonia is responsible for about 19% of all deaths in children aged less than 5 years, of which more than 70% take place in sub-Saharan Africa and south-east Asia. Although based on limited available evidence, recent studies have identified Streptococcus pneumoniae, Haemophilus influenzae and respiratory syncytial virus as the main pathogens associated with childhood pneumonia. Bulletin of the World Health Organization 2008;86:408–416. الرتجمة العربية لهذه الخالصة يف نهاية النص الكامل لهذه املقالة. .Une traduction en français de ce résumé figure à la fin de l’article. Al final del artículo se facilita una traducción al español Introduction the Millennium Development Goal Search strategy and (MDG) 4 of “reducing by two-thirds, 1 selection criteria In the early 1970s Cockburn & Assaad between 1990 and 2015, the under-five generated one of the earliest estimates mortality rate”,6 has generated renewed Most of the morbidity and mortality of the worldwide burden of communi- interest in the development of more estimates in this paper are based on cable diseases. In a subsequent review, accurate assessments of the number 2 work published by CHERG’s pneumo- Bulla & Hitze described the substantial of deaths in children aged less than nia working group.7,8 As a first step, the burden of acute respiratory infections 5 years by cause. Moreover, the moni- group reviewed publications on child- and, in the following decade, with data toring of the coverage of interventions 3 hood pneumonia and created a database from 39 countries, Leowski estimated to control these deaths has become including more than 2200 sources of that acute respiratory infections caused crucial if MDG 4 is to be achieved; information. Further details on the 4 million child deaths each year – 2.6 thus a more accurate establishment of literature search strategies, inclusion million in infants (0–1 years) and 1.4 the causes of deaths in children aged criteria, methods and models used for million in children aged 1–4 years. In less than 5 years becomes crucial. In estimating pneumonia burden were the 1990s, also making use of available 2001, WHO established the Child published elsewhere.7–9 However, the international data, Garenne et al.4 fur- Health Epidemiology Reference Group results of the distribution of global ther refined these estimates by modelling (CHERG) – a group of independent pneumonia episodes by regions and the association between all-cause mortal- technical experts, to systematically countries with the prevalence of expo- ity in children aged less than 5 years and review and improve data collection, sure to main risk factors have not yet the proportion of deaths attributable methods and assumptions underlying been published. Thus, we present the to acute respiratory infection. Results the estimates of the distribution of the details on methods and models used for revealed that between one-fifth and main causes of death for the year 2000. estimating these disaggregated figures one-third of deaths in preschool children In this paper, we summarize the findings in Appendix A (available at: http://www. were due to or associated with acute of this group on the morbidity and mor- respiratory infection. The 1993 World who.int/bulletin/volumes/86/5/07- tality burden of childhood pneumonia. 10–27 Development Report 5 produced figures We also provide new regional and coun- 048769/en/index.html). showing that acute respiratory infection try pneumonia morbidity estimates for caused 30% of all childhood deaths. the year 2000, and review the current Incidence of clinical pneumonia The increasing focus on the reduc- understanding of the distribution of the Rudan et al.8 calculated and published tion of child mortality arising from main etiological agents of pneumonia the first global estimate of the incidence the Millennium Declaration and from among children aged less than 5 years. of clinical pneumonia in children aged a Croatian Centre for Global Health, University of Split Medical School, Soltanska 2, 21000 Split, Croatia. b Child and Adolescent Health and Development, World Health Organization, Geneva, Switzerland. c Department of Epidemiology, Andrija Stampar School of Public Health, Zagreb, Croatia. d Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, England. e University of Edinburgh Medical School, Edinburgh, Scotland. Correspondence to Igor Rudan (e-mail: [email protected]). doi:10.2471/BLT.07.048769 (Submitted: 18 October 2007 – Revised version received: 14 January 2008 – Accepted: 5 March 2008 ) 408 Bulletin of the World Health Organization | May 2008, 86 (5) Special theme – Prevention and control of childhood pneumonia Igor Rudan et al. Epidemiology and etiology of childhood pneumonia less than 5 years for the year 2000. This Table 1. Estimates of incidence and number of new cases per year of clinical estimate was based on the analysis of pneumonia in children aged less than 5 years, by WHO region a data from selected 28 community-based longitudinal studies done in developing WHO region Total population Estimated Estimated no. of countries that were published between aged 0–4 years incidence new cases per year 1969 and 1999. These studies were the (millions) (e/cy) (millions) only sources meeting the predefined African 105.62 0.33 35.13 set of minimum-quality criteria for Americas 75.78 0.10 7.84 8 inclusion in the analysis. The estimated Eastern Mediterranean 69.77 0.28 19.67 median incidence for developing coun- European 51.96 0.06 3.03 tries was 0.28 episodes per child-year, South-East Asia 168.74 0.36 60.95 with an interquartile range 0.21–0.71 Western Pacific 133.05 0.22 29.07 episodes per child-year.8 The variation in incidence between the selected studies Total (developing countries) 523.31 0.29 151.76 was very large, most probably due to the Total (developed countries) 81.61 0.05 4.08 distinct study designs and real differ- Total 604.93 0.26 155.84 ences in the prevalence of risk factors in the various study settings. Given the e/cy, episodes per child-year. substantial uncertainty over the point a Up to 10% of all new cases may progress to severe episodes and require hospitalization. estimate, we used a triangular approach to check for plausibility of our assessment countries account for 74% (115.3 mil- scenario roughly similar to that in the of pneumonia incidence. The ranges lion episodes) of the estimated 156 mil- most developed countries of the world), obtained by the main appraisal and two lion global episodes. More than half of the incidence computed by the model ancillary assessments overlapped between the world’s annual new pneumonia cases was less than 0.05 episodes per child- the values of 148 and 161 million new are concentrated in just five countries year. This estimate is lower than those episodes per year. Giving most weight where 44% of the world’s children aged reported in two classic reports of clinical to the estimate obtained through the less than 5 years live: India (43 million), pneumonia incidence among children main approach, the analyses suggested China (21 million) and Pakistan (10 in the United States of America and in that the incidence of clinical pneumo- million) and in Bangladesh, Indonesia the United Kingdom in the 1970s and nia in children aged less than 5 years in and Nigeria (6 million each). Differ- 1980s, respectively, and is close to our developing countries worldwide (WHO ences in incidence of childhood clinical current estimate for the year 2000 for regions B, D and E; see Annex A) is pneumonia in the world at the country the European Region.28,29 When the close to 0.29 episodes per child-year. level are shown in Fig. 1. prevalence of exposure was set to 99% This equates to 151.8 million new cases Country estimates of the number (an unrealistic scenario at the country every year, 13.1 million (interquartile of clinical pneumonia cases among level, even for the poorest countries range: 10.6–19.6 million) or 8.7% children aged less than 5 years were as- of the world) the incidence computed (7–13%) of which are severe enough to sembled into six WHO regions (African by the model was about 0.77 episodes 8 require hospitalization. In addition, a Region, Region of the Americas, South- per child-year. This estimate is slightly further 4 million cases occur in devel- East Asia Region, European Region, above the upper limit of individually oped countries worldwide (all WHO Eastern Mediterranean Region and reported pneumonia incidence from regions A and Europe regions B and C). Western Pacific Region) as well as into the 28 community-based studies from The regions and their populations are developing and developed regions.

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