PERCH: Pneumonia Etiology Research for Child Health
The PERCH (Pneumonia Etiology Research for Child Health) project is a rigorous multi-country, case-control study of hospitalized pediatric patients with severe lower respiratory tract illnesses (hereafter referred to as pneumonia) to determine the etiology and risk factors associated with the syndrome. Laboratory techniques that have remained vastly unchanged for more than a century have limited our understanding of pneumonia etiology. By applying modern tools with standardized methods, PERCH will contribute to new, precise information to guide the development of new vaccines and treatments.
What are the leading etiologies of pneumonia now?
Many organisms can cause pneumonia. Globally, bacteria such as Hib and pneumococcus are estimated to cause more than 50% of pneumonia deaths in children under 5 years of age (1). Viruses and fungi can also cause pneumonia infections (2).
Why is PERCH needed?
By 2015, three major epidemiological changes will have taken place since the formative etiology studies of the 1980s and these changes make a new examination of pneumonia etiology essential (Scott 2008; Scott and English 2008). First, projections indicate that pneumococcal and Hib conjugate vaccination will be routinely used in 50-90% of all low-income countries, invalidating the underlying evidence base of etiological causes for existing treatment algorithms. Second, HIV-infection, which was absent from studies in the 1980s, is driving both the frequency of pneumonia and the distribution of pathogens causing it. Third, substantial changes in nutrition, urbanization, and access to health care will also modify transmission of agents and the natural history of infection. Without new pneumonia etiology information, our treatment algorithms will be ineffective and we will miss opportunities for prevention with new vaccines, biologics, or other strategies.
The strategy for achieving the goal of sufficient, appropriate information on pneumonia etiology to direct prevention and treatment efforts is complicated by various epidemiologic and microbiologic factors. First, pneumonia, an infection of the lung tissue, ranges in severity and outcome. Second, the pathogens causing pneumonia and the distributions of those pathogens may vary according to severity of the episode. The distribution of pathogens causing mild cases of pneumonia is not the same as that of pathogens causing fatal episodes as evidenced by Hib and PCV vaccine probe studies, as well as studies described above of the etiologic distribution of lung aspirate studies. This suggests either that some pneumonia pathogens are inherently more virulent or that different pathogens contribute to the pathogenesis of pneumonia at different stages of severity. Third, obtaining biologic samples for etiologic testing from the site of infection (the lung) is generally not possible. Fourth, the pathogens causing pneumonia are commonly also observed in the respiratory tracts of humans who do not have pneumonia, making the mere presence of the organism in a child with pneumonia difficult to interpret as causally related. Finally, cases of pneumonia are commonly the consequence of infection by more than one infectious agent.
One consequence of these features is that identification of a pathogen in a case of pneumonia does not necessarily imply that it is the cause of the illness, and conversely, failure to identify a pathogen does not necessarily imply it is unrelated (Murdoch, O'Brien et al. 2009). To establish an etiologic diagnosis it is necessary to consider multiple possible etiologies (exposures) as the cause of any one pneumonia episode. Case-control studies are the design of choice when studying an outcome and its relationship to multiple exposures or risk factors. As such, our approach to estimating the etiologies of hospitalized pneumonia is to conduct a case-control study using modern diagnostics, testing multiple specimens, and determining the proportionate contribution of each using appropriate statistical methods.
PERCH Study Sites and Collaborators
The PERCH project is a large multi-country case-control study of severe pneumonia in hospitalized children under five years of age. Seven PERCH sites have been selected for the study because they represent areas where most of the severe pneumonia cases in children will occur in 2015 and where key interventions are already in place.
PERCH Sample Size: Number of Cases
Updated: January 2014
Collaborating institutions include the University of Witswatersrand in Johannesburg, South Africa, KEMRI Wellcome Trust Research Programme in Kilifi, Kenya, the University of Maryland’s Center for Vaccine Development in Bamako, Mali, the Thailand Ministry of Public Health – United States Centers for Disease Control and Prevention Collaboration’s at two sites in rural Thailand, Boston University at the University Teaching Hospital of Lusaka, Zambia, the Medical Research Council Unit in Basse, The Gambia and the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B) in Dhaka with laboratory testing led by the University of Otago and Canterbury Health Laboratories in Christchurch, New Zealand.
- In settings where these vaccines are not used. O'Brien K, Wolfoson L, Watt J, et al., Burden of Disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates. Lancet. 2009; 374:893-902.
- Mandell Lionel A, Wunderink Richard. Pneumonia. In: Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, Loscalzo J. Harrison's Principles of Internal Medicine (17th ed.) New York: McGraw-Hill, 2008. http://www.accessmedicine.com. Accessed September 7, 2009.