We enrolled a total of 1,892 participants during the overall randomized clinical trial. Of these, 1,772 (93.7%) provided urine and a blood sample at the initial visit, of whom 848 (44.8%) also provided stool samples. The baseline characteristics of these participants are shown in . There was no significant difference in baseline characteristics among participants providing only blood and urine samples and those providing blood, urine, and stool. Of the 1,772 participants providing blood, 251 (14.2%) were HIV infected. A total of 667 (37.6%) participants were infected with P. falciparum; the geometric mean malaria parasite density was 484 parasites/μL (range = 20–106,000 parasites/μL). Among the 848 participants providing blood, stool, and urine, the most commonly identified helminthic infection was S. haematobium (N = 274; 32.3%). An additional 122 (14.4%) and 21 (2.5%) participants were infected with hookworm and S. mansoni, respectively. Ascaris and Trichuris infections occurred rarely (< 0.5%). Sixty-three (7.4%) participants had two or more helminthic infections. The most common combination was hookworm and S. haematobium coinfection (N = 46). Two participants had three or more helminthic infections. The geometric mean egg count was 163 epg for hookworm (range = 24–5,208 epg), 93 epg for S. mansoni (range = 24–600 epg), and 22 eggs/10 mL for S. haematobium (range = 2–252 eggs/10 mL). Among those with hookworm, 95% (N = 116) had light infections; only six (4.9%) infected participants had moderate or heavy hookworm infections. Similarly, most S. haematobium (75.9%) or S. mansoni (57.1%) infections were light.
Baseline characteristics of pregnant women in southern Malawi providing blood, urine, and stool samples
Although mild anemia (hemoglobin < 11 g/dL) was commonly observed (77.5%), severe anemia (hemoglobin < 7 g/dL) was identified in only 34 (4%) participants. Presence of mild anemia was not associated with any of the three most common helminthic infections (S. haematobium, hookworm, and S. mansoni). On univariate analysis, severe anemia was more common among participants infected with hookworm (7.4% versus 3.4%; P < 0.05). However, when other variables associated with anemia were incorporated into a multivariate logistic regression model, only malaria infection, first pregnancy, and elevated temperature (> 37.5°C) at presentation were associated with severe anemia (adjusted odds ratio [aOR] = 2.7, 95% confidence interval [CI] = 1.2–6.1; aOR = 3.7, 95% CI = 1.5–9.1; aOR = 3.3, 95% CI = 1.6–6.8, respectively]; neither helminthic nor HIV infection were significant.
The demographic and clinical characteristics associated with having P. falciparum, hookworm, or S. haematobium infection on univariate analysis are shown in . The characteristics associated with malaria infection in order of the strength of association are first pregnancy, having a pit latrine or no sanitary facility, earthen flooring at home, age < 20 years, exposure to lakes and rivers, mid-upper arm circumference (MUAC) ≤ 25 cm, having a primary school education or less, and weight < 50 kg. Having a job and sleeping under an insecticide-treated bed net (ITN) were associated with a significant reduction in the likelihood of having malaria infection (relative risk [RR] = 0.5, 95% CI = 0.3–0.8; RR = 0.7, 95% CI = 0.5–0.8, respectively). Although 26.9% of participants reported fever during pregnancy, there was no association between reporting fever and malaria parasitemia (47.1% with subjective fever versus 38.2% without subjective fever had malaria parasitemia; P = 0.36). Only 3 of 332 (0.9%) participants with malaria parasitemia had a temperature ≥ 37.5°C.
Demographic and clinical characteristics associated with prevalence of malarial, hookworm, or Schistosoma haematobium infection among 1,772 primi- and secundigravid women in southern Malawi
Associations in prevalence and parasite densities among those with coinfections are shown in and . HIV-infected participants were more likely to have malaria parasitemia (RR = 1.2, 95% CI = 1.00–1.4) and had higher geometric mean malarial parasite densities (721 versus 449 parasites/μL blood; P < 0.005) than those without HIV. However, HIV-positive participants were less likely to have S. haematobium infection (RR = 0.7, 95% = CI 0.5–0.9) and had significantly lower S. haematobium egg counts (17 versus 24 eggs/mL urine; P < 0.05). Malaria infection was more common among participants with hookworm coinfection (RR = 1.6, 95% CI = 1.4–1.9). However, hookworm coinfection was not associated with differences in malaria parasite density (557 versus 473 parasites/μL blood; P = 0.5). In contrast, participants with S. haematobium coinfection had lower malaria parasite densities (410 versus 528 parasites/μL blood; P < 0.05) but were not more likely to be infected with malaria (RR = 1.1, 95% CI = 0.99–1.3).
Coinfections associated with prevalence of malarial, hookworm, or Schistosoma haematobium infection among 1,772 primi- and secundigravid women in southern Malawi
Coinfections associated with malarial, hookworm, or Schistosoma haematobium parasite density among 1,772 primi- and secundigravid women in southern Malawi
We further categorized heminthic infections into single or mixed infections. Hookworm infection alone remained associated with malaria infection (RR = 1.6, 95% CI = 1.3–2.1) compared with no helminthic infection. This same effect was noted even with very light infections (< 100 epg; RR = 1.6, 95% CI = 1.2–2.3). In addition, S. haematobium infection alone or mixed hookworm/S. haematobium infection was associated with greater odds of having malaria infection (RR = 1.2, 95% CI = 1.02–1.5; RR = 1.9, 95% CI = 1.5–2.4, respectively) compared with no helminthic infection.
Hookworm infection alone or mixed hookworm/S. haematobium infection had no apparent association with geometric mean malarial parasite densities compared with no helminthic infection (524 versus 557 parasites/μL blood; P = 0.85; 625 versus 557 parasites/μL blood; P = 0.75, respectively). However, S. haematobium infection alone remained significantly associated with lower geometric mean malarial parasite densities (344 versus 557 parasites/μL blood; P < 0.05) compared with no helminthic infection. No difference in mean malaria parasite density was identified between light and heavy S. haematobium infections.
On multivariate logistic regression analysis (), the characteristics associated with malaria infection in order of the strength of association included mixed hookworm/S. haematobium infection, first pregnancy, earthen flooring at home, hookworm infection alone, HIV infection, exposure to lakes and rivers, and age < 20 years. S. haematobium infection alone was no longer significant when the variable exposure to lakes and rivers was added to the model. As might be expected, sleeping under an ITN remained significantly associated with reductions in malaria infection.
Results of multivariate logistic regression analysis of factors associated with malarial infection among 779 primi- and secundigravid women in southern Malawi*