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The objectives of this study were to estimate the prevalence of atopic sensitization, and to identify common aeroallergens associated with atopic sensitization among women in Entebbe, Uganda, and to determine risk factors for atopic sensitization among those with and without a history of asthma or eczema. A case-control study was conducted within a trial of deworming in pregnancy, approximately 2 years after the intervention. Skin prick test reactivity was assessed among 20 women with a history of asthma, 25 with history of eczema and 95 controls. Overall prevalence of reactivity was estimated by adjusting for the prevalence of asthma in the whole cohort. Overall skin prick test prevalence was: any allergen 30.7%, Blomia tropicalis 10.9%, Dermatophagoides mix 16.8%, cockroach 15.8%. The prevalence of a positive skin prick test was significantly associated with a history of asthma (70% to any allergen vs. 32%, P = 0.002) but not with a history of eczema (44% vs. 36%, P = 0.49). Women with Mansonella perstans had significantly reduced odds for atopic sensitization (adjusted odds ratio 0.14, 95% CI 0.03-0.69); women with a history of asthma were less likely to have hookworm (adjusted odds ratio 0.24, 95% CI 0.07-0.81) but this association was weaker for women with a history of eczema. [Clinical Trial No. ISRCTN32849447]. © 2008 Royal Society of Tropical Medicine and Hygiene.
The study participants were recruited from women in an ongoing trial, the Entebbe Mother and Baby Study (EMABS), in Entebbe and Katabi, a peri-urban area along the shores of Lake Victoria in Uganda. Details of the EMABS trial have been described (Elliott et al., 2007). In summary, pregnant women were recruited from the Entebbe hospital antenatal clinic, a free government facility, during their second or third trimester. Women who fulfilled the trial inclusion criteria and were interested in the study gave written informed consent and were requested to provide a stool sample. Blood samples were also drawn for routine tests (such as haemoglobin level and syphilis serology), for HIV serology, and for examination for malaria parasites and Mansonella perstans (the only common filarial worm in the study area). The women were then enrolled in a double-blind, placebo-controlled trial of treatment of maternal worms in pregnancy with albendazole versus placebo and praziquantel versus placebo in a 2 × 2 factorial design. As part of standard antenatal care at the clinic, all women received intermittent presumptive treatment for malaria with sulfadoxine–pyrimethamine, and HIV-positive women were enrolled in a programme for prevention of mother-to-child HIV transmission using nevirapine. Following delivery, women provided another stool and blood sample and, at 6 weeks post delivery, they all received albendazole and praziquantel. Children continued to attend the study clinic for routine follow up for immunizations in infancy and for quarterly study visits thereafter. An additional questionnaire regarding maternal and family history of allergic disease was administered to mothers attending with their children when the children were 1 year old. Women whose children had reached 1 year or more, and who had responded to the questionnaire on allergic disease, were eligible for recruitment to this study in an unmatched case–control study design. The sample included, as cases, all mothers reporting a history of asthma and or eczema and, as controls, a random sample selected from those who had no such history. The participants gave free and informed written consent. Skin prick testing of the women was conducted at least 1 year after delivery (and at least 10 months after treatment with both albendazole and praziquantel). Tests were performed using standardized extracts from organisms known to be present in the study environment (ALK Abello, Hoersholm, Denmark): Blomia tropicalis; Dermatophagoides mix (D. farinae, D. pteronyssinus); Cynodon dactylon (Bermuda grass); pollen mix (Artemisia, Chenopodium, Parietaria, Plantago); mould mix (Alternaria, Chaetomium, Cladosporium fulvum, Cladosporium herbarum, Fusarium); cat (Felix domesticus) and dog (Canis familiaris) epithelia; and American cockroach (Periplaneta americana). Histamine was used as a positive control and saline solution as the negative control. A mean wheal diameter of at least 3 mm greater than the negative control was taken as positive, with the reading taken after 15 min. Women were scheduled to visit the study clinic when their children were 1 year old. During the visit, the women were asked if they themselves had ever had asthma and or eczema. Asthma has an equivalent term in the local language but eczema does not, so it was described as a recurrent itchy rash associated with a dry or weeping skin affecting predominantly flexures (inside the elbows, behind the knees) and frictional areas such as neck, wrists and ankles, as well as below the buttocks, in the armpits, and around the eyes and ears. We estimated that a sample of 56 cases and 112 controls would have 80% power with 0.05 significance level to detect a difference of 30% versus 10% positive skin prick test among cases and controls respectively, a plausible difference in the light of results obtained elsewhere. This same sample size would also give 80% power to demonstrate skin prick test reactivity to common allergens of 10% (±3.5%) among the study women. Data were collected on pre-coded forms and questionnaires and manually checked before double data entry using Microsoft Access (Microsoft Corp., Redmond, WA, USA). Data were analysed using STATA version 8 (Stata Corp., College Station, TX, USA). Prevalence of skin prick test reactivity to each allergen was calculated separately for cases and controls. To obtain a crude estimate of the overall prevalence of skin prick test reactivity in the trial population, and for the study of the risk factors associated with atopy, six randomly selected women with asthma/eczema were added to the controls to create a reconstituted population with the same prevalence of reported frequency of asthma (6%) as that in the general trial population. Initial comparisons in the reconstituted population and between atopic and non-atopic cases and controls were made using simple tables and χ2 tests. Logistic regression was used to obtain crude and adjusted odds ratios for the associations between atopy and allergic diseases and helminth infection.
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