Vol. 19, No. 3 Printed in Great Britain
International Journal of Epidemiology ©International Epidemiological Association 1990
Malnutrition is Associated with Increased Diarrhoea Incidence and Duration among Children in an Urban Brazilian Slum JOHN B SCHORLING,* JAY F McAULIFFE,*" MARIA AUXIUADORA DE SOUZA,t AND RICHARD LGUERRANT*
Diarrhoea remains one of the most important health problems in developing areas of the world. Children under five years of age have an estimated one billion episodes of diarrhoea per year, which may result in five million deaths.1 An association between nutritional status and diarrhoea has long been postulated.2 There is general agreement that more diarrhoea results in worsened nutritional status.3"6 However, the nature of the inverse relationship is less clear. A number of investigations have shown that children with poorer nutritional status have longer diarrhoeal episodes than better nourished children.710 The results with regard to incidence are more equivocal. Several studies from Bangladesh have shown no association, including those of Chen et al.," and Black et al.,7 while studies from Nigeria,12 Costa Rica,8 and Guatemala13 have demonstrated a higher incidence of diarrhoea among •Division of Geographic Medicine, University of Virginia School of Medicine, Charlottesville. Virginia, USA. "Project Hope/Brazil, Fortalcza. Ceara. Brazil. tDepartment of Community Medicine. Federal University of Ceara. Fortaleza, Ceara, Brazil. Reprint requests to: John B Schorling, Box 494. Department of Medicine, University of Virginia Health Sciences Center. Charlottesville, VA 22908, USA.
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more poorly nourished children. Recently, these studies have been criticized for their methodological shortcomings, especially analyses in which multiple observations from individual children have been considered to represent independent events. Bairagi et al.,9 addressed this issue by considering the relationship between malnutrition and diarrhoea for single time periods for each child, and they found no association. Two other recent studies used an autoregression term to control for the occurrence of diarrhoea during previous periods of observation.1415 Both demonstrated that worsened nutritional status was a risk factor for subsequent diarrhoea. Thus, whether malnutrition predisposes children to more episodes of diarrhoea remains unclear. A separate issue is how long children of poorer nutritional status might be at risk for increased diarrhoea. Most studies have analysed discrete two- or threemonth periods. Several researchers have analysed longer intervals and have found no association,912"14 although Chen et al.,'6 did note that severe malnutrition increased the risk of death from all causes among children over a two-year period. Thus, whether nutritional status determined at one point in time predicts
Downloaded from http://ije.oxfordjournals.org/ at Emory University on August 17, 2015
Schorling J B (Division of Geographic Medicine, University of Virginia School of Medicine, Charlottesville, Virginia, USA), McAuliffe J F, de Souza M A and Guerrant R L Malnutrition is associated with increased diarrhoea incidence and duration among children in an urban Brazilian Slum. Internationa/Journal of Epidemiology, 1990, 19: 728-735. This study was undertaken to further define the relationship between malnutrition and subsequent diarrhoeal illness among children. A cohort of 61 children under five years of age was followed for two years in an urban Brazilian slum. Nutritional status was determined at two-month intervals and was used to predict the subsequent occurrence of diarrhoea. A significant, graded association between worsened nutritional status, as measured by length- or weightfor-age, and diarrhoea incidence was found. This relationship was present for both two-month and one-year periods following nutritional assessment. The average duration of diarrhoea was also significantly longer during the twomonth periods which were preceded by the worst nutritional status. Overall, the most malnourished children had nearly twice the total number of days of diarrhoea that better nourished children had. These results provide additional evidence that a significant association between malnutrition and both increased diarrhoea incidence and duration exists.
MALNUTRITION AND DIARRHOEA
the occurrence of diarrhoea for more than a few months is unknown. There were several purposes of the present study. The first was to determine whether an association existed between nutritional status and the subsequent incidence, average duration, and prevalence of diarrhoeal illness among a cohort of children in an urban Brazilian slum. The second was to determine the duration of any association after the initial nutritional classification.
Illness Surveillance and Nutritional Assessment Each participating home was visited thrice weekly by trained community health workers to determine the occurrence of diarrhoea. Diarrhoea was defined as decreased stool consistency and increased frequency as noted by their caregivers. Discrete episodes were separated by at least three diarrhoea-free days. The length and weight of all children were determined monthly by the same four trained medical students. Lightlyclothed weights to the nearest 0.1 kg were obtained using a calibrated sling scale. Length was measured supine to the nearest centimetre. Data Analysis The number of episodes, average duration per episode, and the total number of days of diarrhoea were computed for 12 non-overlapping two-month periods for each child. All days for an episode that began in one period and extended into the next were attributed to the first period, as was the episode itself. Weight and
length determined at the start of each period were used to predict the subsequent occurrence of diarrhoea during that period. The CDC Anthropometric Software Package18 was used to compute weight-for-age, length-for-age, and weight-for-length Z-scores. The anthropometric indicators were classified as suggested by Waterlow." When there was missing nutritional data for any period, only that period was excluded from the analysis. The association between nutritional status and diarrhoea was analysed using multiple regression. Individual equations were constructed for weight-for-age and length-for-age Z-scores versus the following dependent variables: total number of episodes in the twomonth period; average duration of each episode; and total days of diarrhoea during the period. The average duration of diarrhoea and total number of days per period were logarithmically transformed (base 10). This normalized the distributions of these variables and equalized the variances between categories. The nutritional indicators were included in the regression equations as both continuous and dichotomous variables. For length-for-age, two dichotomous classifications were used, since the level at which the number of episodes appeared to increase (
International Journal of Epidemiology ©International Epidemiological Association 1990
Malnutrition is Associated with Increased Diarrhoea Incidence and Duration among Children in an Urban Brazilian Slum JOHN B SCHORLING,* JAY F McAULIFFE,*" MARIA AUXIUADORA DE SOUZA,t AND RICHARD LGUERRANT*
Diarrhoea remains one of the most important health problems in developing areas of the world. Children under five years of age have an estimated one billion episodes of diarrhoea per year, which may result in five million deaths.1 An association between nutritional status and diarrhoea has long been postulated.2 There is general agreement that more diarrhoea results in worsened nutritional status.3"6 However, the nature of the inverse relationship is less clear. A number of investigations have shown that children with poorer nutritional status have longer diarrhoeal episodes than better nourished children.710 The results with regard to incidence are more equivocal. Several studies from Bangladesh have shown no association, including those of Chen et al.," and Black et al.,7 while studies from Nigeria,12 Costa Rica,8 and Guatemala13 have demonstrated a higher incidence of diarrhoea among •Division of Geographic Medicine, University of Virginia School of Medicine, Charlottesville. Virginia, USA. "Project Hope/Brazil, Fortalcza. Ceara. Brazil. tDepartment of Community Medicine. Federal University of Ceara. Fortaleza, Ceara, Brazil. Reprint requests to: John B Schorling, Box 494. Department of Medicine, University of Virginia Health Sciences Center. Charlottesville, VA 22908, USA.
728
more poorly nourished children. Recently, these studies have been criticized for their methodological shortcomings, especially analyses in which multiple observations from individual children have been considered to represent independent events. Bairagi et al.,9 addressed this issue by considering the relationship between malnutrition and diarrhoea for single time periods for each child, and they found no association. Two other recent studies used an autoregression term to control for the occurrence of diarrhoea during previous periods of observation.1415 Both demonstrated that worsened nutritional status was a risk factor for subsequent diarrhoea. Thus, whether malnutrition predisposes children to more episodes of diarrhoea remains unclear. A separate issue is how long children of poorer nutritional status might be at risk for increased diarrhoea. Most studies have analysed discrete two- or threemonth periods. Several researchers have analysed longer intervals and have found no association,912"14 although Chen et al.,'6 did note that severe malnutrition increased the risk of death from all causes among children over a two-year period. Thus, whether nutritional status determined at one point in time predicts
Downloaded from http://ije.oxfordjournals.org/ at Emory University on August 17, 2015
Schorling J B (Division of Geographic Medicine, University of Virginia School of Medicine, Charlottesville, Virginia, USA), McAuliffe J F, de Souza M A and Guerrant R L Malnutrition is associated with increased diarrhoea incidence and duration among children in an urban Brazilian Slum. Internationa/Journal of Epidemiology, 1990, 19: 728-735. This study was undertaken to further define the relationship between malnutrition and subsequent diarrhoeal illness among children. A cohort of 61 children under five years of age was followed for two years in an urban Brazilian slum. Nutritional status was determined at two-month intervals and was used to predict the subsequent occurrence of diarrhoea. A significant, graded association between worsened nutritional status, as measured by length- or weightfor-age, and diarrhoea incidence was found. This relationship was present for both two-month and one-year periods following nutritional assessment. The average duration of diarrhoea was also significantly longer during the twomonth periods which were preceded by the worst nutritional status. Overall, the most malnourished children had nearly twice the total number of days of diarrhoea that better nourished children had. These results provide additional evidence that a significant association between malnutrition and both increased diarrhoea incidence and duration exists.
MALNUTRITION AND DIARRHOEA
the occurrence of diarrhoea for more than a few months is unknown. There were several purposes of the present study. The first was to determine whether an association existed between nutritional status and the subsequent incidence, average duration, and prevalence of diarrhoeal illness among a cohort of children in an urban Brazilian slum. The second was to determine the duration of any association after the initial nutritional classification.
Illness Surveillance and Nutritional Assessment Each participating home was visited thrice weekly by trained community health workers to determine the occurrence of diarrhoea. Diarrhoea was defined as decreased stool consistency and increased frequency as noted by their caregivers. Discrete episodes were separated by at least three diarrhoea-free days. The length and weight of all children were determined monthly by the same four trained medical students. Lightlyclothed weights to the nearest 0.1 kg were obtained using a calibrated sling scale. Length was measured supine to the nearest centimetre. Data Analysis The number of episodes, average duration per episode, and the total number of days of diarrhoea were computed for 12 non-overlapping two-month periods for each child. All days for an episode that began in one period and extended into the next were attributed to the first period, as was the episode itself. Weight and
length determined at the start of each period were used to predict the subsequent occurrence of diarrhoea during that period. The CDC Anthropometric Software Package18 was used to compute weight-for-age, length-for-age, and weight-for-length Z-scores. The anthropometric indicators were classified as suggested by Waterlow." When there was missing nutritional data for any period, only that period was excluded from the analysis. The association between nutritional status and diarrhoea was analysed using multiple regression. Individual equations were constructed for weight-for-age and length-for-age Z-scores versus the following dependent variables: total number of episodes in the twomonth period; average duration of each episode; and total days of diarrhoea during the period. The average duration of diarrhoea and total number of days per period were logarithmically transformed (base 10). This normalized the distributions of these variables and equalized the variances between categories. The nutritional indicators were included in the regression equations as both continuous and dichotomous variables. For length-for-age, two dichotomous classifications were used, since the level at which the number of episodes appeared to increase (
