DIARRHEAL diseases.

The annual number of deaths from diarrheal diseases among the 0–4 year age group in lowand middle-income countries (LMICs) has dropped by 89 percent, from 4.6 million in 1980 to 526,000 in 2015 (Liu, Hill and others 2016). This striking improvement occurred without vaccines against the major pathogens, except for rotavirus, which is now being scaled-up in LMICs. The incidence of diarrhea has not significantly diminished, especially in young infants (Fischer Walker and others 2012). Therefore, success in reducing mortality appears to be driven largely by improved management rather than prevention (box 9.1). Each day, 4.7 million episodes of diarrheal disease occur, including 100,000 cases of severe diarrhea, along with nearly 1,600 deaths, approximately 9 percent of the mortality in children under age five years (chapter 4 in this volume, Liu, Oza, and others 2016). Increasing awareness of the adverse effects of nonfatal episodes of diarrhea on infant and childhood growth and development, particularly the role of repeated illness and the potential impact of frequent subclinical infections with the same pathogens, presents a new challenge. Interventions will depend on enhanced understanding of causal pathways, pathogenesis, and sequelae of these infections, with or without symptomatic diarrhea. Diarrheal diseases are good indicators of the stage of development of communities in LMICs because of the impact of proximal and distal determinants of diarrheal morbidity and mortality, including the availability of safe drinking water; sanitation; level of education, particularly of mothers; income; food security; nutrition; and access to health care, both preventive and therapeutic. Continued progress depends on recognition that intersectoral interventions are integral to required measures to reduce or eliminate diarrheal diseases as a public health concern. This chapter explores the still-limited evidence on subclinical infections due to known microbial causes of diarrhea, and impacts on intestinal physiology, nutrient absorption, and nutritional status as plausible mechanisms underlying growth stunting and developmental delays. The potential interventions for clinical and subclinical intestinal infections are not necessarily identical, although they undoubtedly overlap. Accordingly, we consider epidemiology, transmission, and mechanisms of disease, as well as social and cultural factors instrumental in determining outcomes. Nutritional needs of infants and young children, breastfeeding practices, use of complementary foods, and management of nutritional rehabilitation of acute malnutrition are covered in greater depth in Das and others (2016, chapter 12 of this volume).