Estimating the Burden of Global Mortality in Children Aged <5 Years by Pathogen-Specific Causes

To the Editor—Globally, infectious diseases account for more than one-half of all deaths among children aged <5 years. Knowledge of the burden of mortality associated with individual pathogens is important for targeting interventions, managing and planning health care services, and guiding research and training priorities. A limitation of the current approach to estimating and reporting global mortality among children aged <5 years is that major causes of deaths are typically presented as a mixture of both pathogen-specific causes (e.g., tuberculosis or HIV infection) and clinical syndromes (e.g., respiratory infections or diarrheal diseases). Although the reporting of mortality statistics from developing countries by clinical syndrome is often pragmatic given the lack of diagnostic tools and vital registration data, it means that the health impact of individual pathogens may not be fully appreciated and the contribution of specific pathogens to global or regional mortality is not specified.

To highlight this issue, we present estimates of global mortality among children aged <5 years by pathogen-specific causes (figure 1), using available World Health Organization Global Burden of Disease data from 2002 (compiled from vital registration data, epidemiological studies, verbal autopsies, disease surveillance systems, and analyses from World Health Organization technical programs) [1–3]. Most deaths among children aged <5 years were due to infectious diseases; infectious diseases accounted for 64% of deaths globally and 81% in the Africa region [1]. More than one-half of these deaths were attributed to “respiratory infections” (26%) and “diarrheal diseases” (24%). However, when data are presented by specific etiology, the following 5 pathogens account for nearly one-half of infection-related deaths (figure 1): Plasmodium falciparum, Streptococcus pneumoniae, rotavirus, measles virus, and Haemophilus influenzae type b.

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Figure 1

Infection-related global mortality among children aged <5 years by pathogen-specific cause, based on figures from the World Health Organization Global Burden of Disease 2002 estimates [1, 2]. Infection-related deaths accounted for 64% of all deaths in children aged <5 years [1]. Of child deaths from respiratory infection, 41% were attributed to Streptococcus pneumoniae, and 22% were attributed to Haemophilus influenzae type b (Hib). The estimated proportion of diarrheal deaths caused by rotavirus was 25% [2].

The value of presenting child mortality data by pathogen-specific cause is well illustrated by examining the relative contribution of P. falciparum to child mortality. Nearly all malaria deaths are due to P. falciparum. Malaria is typically ranked fourth after neonatal disorders, acute respiratory infections, and diarrheal diseases as a major cause of childhood mortality. However, when mortality is broken down according to pathogen-specific cause, P. falciparum is rivaled only by S. pneumoniae as the leading single cause of child mortality. Commercial vaccines are currently available for measles virus, rotavirus, S. pneumoniae, and H. influenzae type b and are being provided to developing countries through the Global Alliance for Vaccines and Immunization and other organizations. Increasing availability of these vaccines may result in an increase in the relative contribution of P. falciparum to child mortality. Issues such as this can only be appreciated when child mortality data are presented by pathogen-specific cause, which also highlights P. falciparum as the major pathogen for which a vaccine is not available.

Presenting child mortality estimates by pathogen-specific cause emphasizes the significant impact made by a small number of individual pathogens and could facilitate planning, implementation, and evaluation of preventative interventions and guide funding, training, and research priorities. Although there are major deficiencies in the data available on pathogen-specific causes of child death, available data sources (including vaccine and intervention studies) can be used to derive informative estimates. More complete data on pathogen-specific mortality, particularly in countries with high childhood mortality, are greatly needed.

• © 2008 by the Infectious Diseases Society of America