Article Figures & Data
Figures
- FIG. 1.
Distribution of growth-inhibitory activities in the study cohort. The histogram shows the growth-inhibitory activities for the 220 study participants measured just prior to the malaria season. Inhibitory activities ranged from −7% to 97.6%, with a median of 26.0%. Only one individual had a negative value for % growth inhibition (−7% [data not shown]).
- FIG. 2.
Growth-inhibitory activity by age group and whether individuals were parasitemic with P. falciparum just prior to the malaria season. Box-and-whisker plots represent the smallest and largest (whiskers), the lower and upper quartiles of (top and bottom of box), and the median (horizontal line across box) growth-inhibitory activity. Growth-inhibitory activity in nonparasitemic individuals increased with age (P < 0.001). Within each age group, the median growth-inhibitory activity was higher in parasitemic than in nonparasitemic individuals, but this difference reached statistical significance only in the 2- to 4-year-old (P < 0.01) and 8- to 10-year-old (P = 0.02) age groups, as indicated by an asterisk above the bar. Sample sizes for nonparasitemic individuals were as follows: 2- to 4-year-olds, n = 68; 5- to 7-year-olds, n = 45; 8- to 10-year-olds, n = 45; and 18- to 25-year-olds, n = 46. Those for parasitemic individuals were as follows: 2- to 4-year-olds, n = 4; 5- to 7-year-olds, n = 4; 8- to 10-year-olds, n = 5; and 18- to 25-year-olds, n = 3. The nonparametric Kruskal-Wallis test was used for statistical analysis.
- FIG. 3.
Kaplan-Meier estimates of the cumulative probability of malaria in children aged 2 to 10 years during the 6-month malaria season, by whether growth-inhibitory activity was greater or less than 40%. Malaria was defined as an axillary temperature of ≥37.5°C, P. falciparum asexual parasitemia of ≥5,000 parasites/μl, and a nonfocal physical examination by the study physician. The number of individuals at risk for the first malaria episode in the two groups over the course of the study period is shown below the plot. The P value was obtained using the log rank test.
- FIG. 4.
Distribution of growth-inhibitory activities in malaria-immune (no malaria episodes) and susceptible (≥1 malaria episode) children aged 2 to 10 years. Malaria was defined as an axillary temperature of ≥37.5°C, P. falciparum asexual parasitemia of ≥5,000 parasites/μl, and a nonfocal physical examination by the study physician.
Tables
- TABLE 1.
Baseline characteristics of the study cohort
Characteristic Value for age group Value for all participants (n = 225) 2-4 yr (n = 73) 5-7 yr (n = 52) 8-10 yr (n = 51) 18-25 yr (n = 49) Gender (no. [%] of females) 42 (57.5) 25 (48.1) 19 (37.3) 30 (61.2) 116 (51.6) Ethnicity (no. [%]) Bambara 48 (65.8) 26 (50.0) 27 (53.0) 33 (67.4) 134 (59.6) Sarakole 21 (28.8) 23 (44.2) 20 (39.2) 13 (26.5) 77 (34.2) Fulani 3 (4.1) 3 (5.8) 3 (5.9) 2 (4.1) 11 (4.9) Malinke 1 (1.4) 0 (0.0) 1 (2.0) 1 (2.0) 3 (1.3) No. (%) of individuals with P. falciparum-positive smear at enrollment 4 (5.5) 4 (7.7) 5 (9.8) 3 (6.1) 16 (7.1) Level of parasitemia if smear was positive at enrollment (no. of parasites/μl) (geometric mean [95% CI]) 1,438 (159-12,973) 3,616 (1,500-8,715) 415 (134-1,287) 953 (39-23,382) 1,137 (579-2,232) No. (%) of individuals positive for gastrointestinal helminths at enrollmenta 9 (13.0) 4 (8.3) 4 (9.3) 0 (0.0) 17 (9.0) No. (%) of individuals positive for urine schistosomiasis at enrollmentb 0 (0.0) 0 (0.0) 2 (4.3) 9 (28.1) 11 (6.0) Hemoglobin level at enrollment (g/l) (mean ± SD) 11.2 ± 1.2 11.8 ± 1.0 12.3 ± 1.1 13.6 ± 1.4 12.1 ± 1.5 Distance lived from clinic (km) (mean ± SD) 0.39 ± 0.11 0.40 ± 0.14 0.37 ± 0.10 0.36 ± 0.09 0.38 ± 0.11 No. (%) of individuals who used bed netsc 21 (28.8) 16 (30.8) 9 (17.6) 15 (30.6) 61 (27.1) No. (%) of individuals with hemoglobin typed AA 50 (72.5) 43 (86.0) 35 (68.6) 32 (76.2) 160 (75.5) AS 8 (11.6) 4 (8.0) 5 (9.8) 5 (11.9) 22 (10.4) AC 10 (14.5) 3 (6.0) 11 (21.6) 5 (11.9) 29 (13.7) CC 1 (1.5) 0 (0.0) 0 (0.0) 0 (0.0) 1 (0.5) - TABLE 2.
Malaria-related clinical outcomes during the 9-month study period, by age group
Outcome Value for age group Value for all individuals (n = 225) P valuea 2-4 yr (n = 73) 5-7 yr (n = 52) 8-10 yr (n = 51) 18-25 yr (n = 49) Malaria incidence (mean ± SD)b 1.99 ± 1.25 1.94 ± 1.21 0.98 ± 1.05 0.08 ± 0.28 1.33 ± 1.30 <0.001 No. of cases of severe malariac 4 1 0 0 5 Time to first malaria episode for those who experienced malaria (days [median])d 101 114 130 153 115 0.02 No. (%) of individuals with at least one malaria episode 63 (86.3) 45 (86.5) 31 (60.8) 4 (8.2) 143 (63.6) <0.001 Level of parasitemia at first malaria episode (no. of parasites/μl) (geometric mean [95% CI]) 34,374 (24,955-47,348) 15,687 (9,623-25,574) 10,433 (5,079-21,427) 8,816 (4,082-19,037) 19,625 (15,004-25,668) 0.04 ↵ a P values were derived by using Fisher's exact test for categorical variables and the Kruskal-Wallis test for continuous variables.
↵ b A malaria episode was defined as a temperature of >37.5°C, asexual parasitemia of >5,000 parasites/microliter, and nonfocal physical examination.
↵ c According to WHO definition of severe malaria.
↵ d Days since study enrollment.
- TABLE 3.
Results of multivariate regression analysis for children aged 2 to 10 years
Explanatory variable Result of regression analysis for malaria outcome Whether malaria was experienced Time to first malaria episode Malaria incidence OR (95% CI) P HR (95% CI) P IRR (95% CI) P Age (yr) 0.78 (0.63-0.95) 0.02 0.86 (0.80-0.94) <0.001 0.91 (0.86-0.96) 0.001 Gender 2.04 (0.76-5.46) 0.16 1.38 (0.94-2.03) 0.10 1.03 (0.82-1.30) 0.80 Ethnicity, Bambara 0.23 (0.03-2.08) 0.19 0.68 (0.34-1.34) 0.26 1.12 (0.79-1.58) 0.52 Ethnicity, Sarakole 0.84 (0.08-8.96) 0.89 1.00 (0.49-2.06) 0.99 1.53 (1.07-2.18) 0.02 Distance lived from clinic (km) 0.30 (0.004-24.02) 0.59 0.48 (0.07-3.23) 0.45 0.77 (0.23-2.59) 0.67 Bed-net usea 0.70 (0.25-1.97) 0.50 0.89 (0.59-1.35) 0.59 0.96 (0.75-1.23) 0.77 HbAS type 0.23 (0.06-0.87) 0.03 0.41 (0.21-0.79) 0.01 0.43 (0.27-0.68) <0.001 HbAC type 0.56 (0.16-1.95) 0.36 0.81 (0.47-1.40) 0.44 1.14 (0.80-1.63) 0.47 Growth-inhibitory activityb 0.50 (0.30-0.85) 0.01 0.80 (0.63-1.02) 0.07 0.93 (0.75-1.16) 0.53 ↵ a Nightly bed-net use was self-reported at the end of the malaria season.
↵ b For this analysis, growth-inhibitory activity was divided into deciles, and thus the regression coefficient for this variable represents the change in malaria risk with each 10% increase in growth-inhibitory activity, holding all other independent variables constant.
