2. Variation in morbidity from infectious disease

It is an epidemiological truism that disease morbidity varies with time, place, and person. All this means is that in some places infections may be highly prevalent and in others less so. Even within the same place, overall morbidity and the kinds of infections responsible change over time. Finally, there is great variability among individuals, even at the same time and place. The first step is to identify representative burdens of morbidity as a basis for estimating the effect of infection under any given set of circumstances.

Figures 1 to 3 from Guatemala (MATA, 1978), Mexico (CHAVEZ and MARTINEZ, 1982), and The Gambia (ECCLES et al., 1989), respectively, illustrate the high frequency of infections in young children under village conditions in developing countries. Table 2 provides evidence for the frequency of infections among infants in The Gambia. Each episode of infection is associated with adverse nutritional consequences ranging from mild to severe.

Figure 1. Weight, infections and infectious diseases in a male child. Top: Solid line represents weight of child; broken line is median of the standard. Length of each horizontal line indicates duration of infectious disease. Each mark shows a week positive for the particular infectious agent. Bottom: Observed weight increments (vertical bars) and expected median increments of the standard (dots). (MATA et al. 1971)

Figure 2. The non-supplemented, from the third to the fifth semester, have some illness for as much as half the time. Teozonteopan, Mexico. (CHAVEZ and MARTINEZ, 1979)

Figure 3. The changes in sleeping and metabolic rate (SMR) and body weight with time. Blocks represent the duration of acute episodes of infection. (URTI: upper respiratory tract infection; UTI: urinary tract infection). Gambia. (ECCLES, COLE and WHITEHEAD, 1989)

Table 2. Number of episodes of each illness and the number of days involved for 7 infants in rural Gambia

Illness (episodes/d)	Infant
	1	2	3	4	5	6	7
URTI +	6/31	1/3	6/29	1/6	3/24	2/11	3/24
Tonsilitis	1/5	-	1/6	-	2/7	-	-
Otitis media	2/11	8/50	2/8	-	2/11	6/35	1/5
Pneumonia	2/9	-	-	-	2/9	-	1/3
Diarrhea *	3/17	2/18	7/39	1/7	-	2/17	1/12
Diarrhea & vomiting *	-	1/4	1/11	1/4	1/5	1/16	1/5
Vomiting *	-	-	-	-	-	-	1/6
Malaria	1/3	-	1/3	-	-	-	-
Abscess	1/6	-	-	-	1/7	-	-
UTI +	-	-	-	-	1/6	-	-
Fever	2/9	-	3/17	1/7	4/17	1/5	-
All illnesses	18/91	12/75	21/113	4/24	16/86	12/84	8/55

+ URTI = Upper respiratory tract infection; UTI = Urinary tract infection
* Grouped in the analysis as 'gastro-enteritis'.
(ECCLES, COLE and WHITEHEAD, 1989)

Table 3 shows that children in Guatemala who have had measles in preceding weeks have a marked loss of lean body mass compared with children in the same village who did not experience this disease (INCAP, unpublished data). Figure 4 illustrates the devastating effect of whooping cough in a poorly nourished Guatemalan who required 26 weeks after onset of the disease for her weight to return to that before the onset, leaving the child further retarded in weight for age (MATA, 1978). Table 4 shows that, of 44 cases of whooping cough in his village, 25% of the children required more than 25 weeks to regain initial weight, and only one-third recovered in 8 weeks or less. The effect of diarrheal infections on weight gain is shown in Figure 5 (MARTORELL et al., 1975). The degree of deficit in growth increment is proportional to the number of days ill with diarrhea in children 0- to 7-years-old.

Table 3. Effect of measles on CHI index in children in Guatemalan village compared with children with kwashiorkor from the region

Village children	.90-1.00
Children with recent measles	.70-.80
Kwashiorkor	.60 -.70

CHI = Creatine per cm ht (unpublished INCAP data)

Table 4. Time required to recover the weight lost from a single episode of whooping cough

Weeks	N	%
0-4	6	14
5-8	8	18
9-12	8	18
13-16	4	9
17-24	7	16
25 +	11	25
Total	44	100

(INCAP, 1968)

Figure 4. Deterioration of the nutritional status of female child after an attack of whooping cough. Broken top line corresponds to the INCAP standard; solid line shows the mean weight curve for Cauque children; bottom broken line is observed weights of the child. O = onset of disease; A = weight loss; B = weight gain expected in period equivalent to the length of recuperation if not attacked by the disease. To estimate this amount, the mean weight curve for Cauque children was used; the curve of the child was assimilated to such a curve at the time of onset.

Figure 5. Days ill with diarrhea and growth retardation in stature. 134 children, 0-7 years, in rural Guatemalan villages.

In most developing country populations, the close relationships among poverty, malnutrition, poor sanitation and hygiene, and the high prevalence of infections act synergistically to increase the risk of malnutrition and growth failure.

While infectious disease prevalence rates are high under village conditions in developing countries, they are even higher when children are brought together in institutions. Table 5 lists 108 infectious episodes among 34 children in a model convalescent home in Guatemala City with good sanitation and ample room (VITERI, personal communication). Table 6 records 136 episodes among 60 children in a 6-month feeding study in an orphanage in Vellore, India (PEREIRA, personal communication). These are only examples of a universal phenomenon. In addition, children in nurseries, even in industrialized countries, are susceptible to epidemics of a single infection.

Table 5. Acute infections among 32 children aged 2 to 9 years observed in a 'model' convalescent home in Guatemala City for 90 days

Diseases	Total No. episodes	Diseases	Total No. episodes
Infectious hepatitis	2	Gonococcal vaginitis	11
Measles	2	Purulent otitis media	4
Bronchopneumonia	3	Acute tonsillitis	7
Bronchial asthma and asthmatic bronchitis	15	Upper respiratory tract infection	15
Gastroenteritis	5	Fever of unknown origin	9
Amebiasis	9	Urinary infection	1
Parotitis	4	Impetigo and cellulitis	13
Chickenpox	3	Skin allergy	5

Table 6. Illnesses among 60 children aged 2 to 9 years in a 6-month orphanage feeding study in Vellore, South India

Respiratory infections	43
Fever	24
Diarrhea/dysentery	14
Skin infection	47
Jaundice	4
Conjunctivitis	1
Gingivitis	3
Total	136

(PEREIRA, personal communication)