Assessing the Impact of Misclassification Error on an Epidemiological Association between Two Helminthic Infections

Hookworm, roundworm, and whipworm are collectively known as soil-transmitted helminths. These worms are prevalent in most of the developing countries along with another parasitic infection called schistosomiasis. The tests commonly used to detect infection with these worms are less than 100% accurate. This leads to misclassification of infection status since these tests cannot always correctly indentify infection. We conducted an epidemiological study where such a test, the Kato-Katz technique, was used. In our study we tried to show how misclassification error can influence the association between soil-transmitted helminth infection and schistosomiasis in humans. We used a statistical technique to calculate epidemiological measures of association after correcting for the inaccuracy of the test. Our results show that there is a major difference between epidemiological measures of association before and after the correction of the inaccuracy of the test. After correction of the inaccuracy of the test, soil-transmitted helminth infection was found to be associated with increased risk of acquiring schistosomiasis. This has major public health implications since effective control of one worm can lead to reduction in the occurrence of another and help to reduce the overall burden of worm infection in affected regions

A cross-sectional study of the prevalence of intensity of infection with Schistosoma japonicum in 50 irrigated and rain-fed villages in Samar Province, the Philippines

BACKGROUND: Few studies have described heterogeneity in Schistosoma japonicum infection intensity, and none were done in Philippines. The purpose of this report is to describe the village-to-village variation in the prevalence of two levels of infection intensity across 50 villages of Samar Province, the Philippines. METHODS: This cross-sectional study was conducted in 25 rain-fed and 25 irrigated villages endemic for S. japonicum between August 2003 and November 2004. Villages were selected based on irrigation and farming criteria. A maximum of 35 eligible households were selected per village. Each participant was asked to provide stool samples on three consecutive days. All those who provided at least one stool sample were included in the analysis. A Bayesian three category outcome hierarchical cumulative logit regression model with adjustment for age, sex, occupation and measurement error of the Kato-Katz technique was used for analysis. RESULTS: A total of 1427 households and 6917 individuals agreed to participate in the study. A total of 5624 (81.3%) participants provided at least one stool sample. The prevalences of those lightly and at least moderately infected varied from 0% (95% Bayesian credible interval (BCI): 0%–3.1%) to 45.2% (95% BCI: 36.5%–53.9%) and 0% to 23.0% (95% BCI: 16.4%–31.2%) from village-to-village, respectively. Using the 0–7 year old group as a reference category, the highest odds ratio (OR) among males and females were that of being aged 17–40-year old (OR = 8.76; 95% BCI: 6.03–12.47) and 11–16-year old (OR = 8.59; 95% BCI: 4.74–14.28), respectively. People who did not work on a rice farm had a lower prevalence of infection than those working full time on a rice farm. The OR for irrigated villages compared to rain-fed villages was 1.41 (95% BCI: 0.50–3.21). DISCUSSION: We found very important village-to-village variation in prevalence of infection intensity. This variation is probably due to village-level variables other than that explained by a crude classification of villages into the irrigated and non-irrigated categories. We are planning to capture this spatial heterogeneity by updating our initial transmission dynamics model with the data reported here combined with 1-year post-treatment follow-up of study participants

Implementation of the Connective Tissue Screening Questionnaire in Northeast Pennsylvania to Identify Comorbidities of Connective Tissue Diseases in Subjects With Systemic Lupus Erythematosus

Previous studies have described an increased risk of developing an additional connective tissue disease (CTD) when one such ailment is present. We examine here the likelihood that individuals with systemic lupus erythematosus (SLE) screen positive for one or more of the following five autoimmune CTDs: Sjögren’s syndrome, scleroderma, rheumatoid arthritis, dermatomyositis/polymyositis, and mixed connective tissue disorder. Five hundred SLE-diagnosed subjects were asked to complete a CTD screening questionnaire (CSQ). The results were analyzed according to the set of diagnostic criteria given by the American College of Rheumatology to identify probable cases of each CTD. Significant standardized prevalence ratios and comorbidities indicate an increased risk for the other autoimmune CTDs. In all, 96% of the subjects screened positive for at least one additional CTD, and 13% screened positive for at least two additional CTDs. We see that the SLE-diagnosed population may benefit from further attention regarding the presence of additional CTDs, which may further inform treatment strategies. We also see the application of the CSQ as a potentially important tool for clinical practice, and we describe the present study’s limitations along with possible ways that these can be addressed

Cross-sectional associations between intensity of animal and human infection with Schistosoma japonicum in Western Samar province, Philippines.

OBJECTIVE: To estimate the association between the intensity of animal infection with Schistosoma japonicum and human infection in Western Samar province, the Philippines. METHODS: We conducted an observational cross-sectional study of 1425 households in 50 villages. Stool samples were collected on each of 1-3 days from 5623 humans, 1275 cats, 1189 dogs, 1899 pigs, 663 rats and 873 water buffalo. Intensity of infection with S. japonicum was measured by the number of eggs per gram (EPG). Egg counts were done using the Kato-Katz method. We used a Bayesian hierarchical cumulative logit model, with adjustments for age, sex, occupation and measurement error. FINDINGS: The adjusted proportions of humans lightly infected (classified as 1-100 EPG) was 17.7% (95% Bayesian credible interval = 15.3-20.2%); the proportion classified as at least moderately infected (>100 EPG) was 3.2% (2.2-4.6%). The crude parasitological results for animals indicated that 37 cats (2.9%), 228 dogs (19.2%), 39 pigs (2.1%), 199 rats (30.0%) and 28 water buffalo (3.2%) were infected. In univariate analyses the odds ratios corresponding to a unit increase in the mean number of EPG at the village-level in dogs was 1.05 (1.01-1.09), in cats 1.35 (1.02-1.78), in pigs 1.16 (0.24- 5.18) and in rats 1.00 (1.00-1.01). Mean EPG values in cats, dogs, pigs and rats were correlated with one another. This confounding made interpreting the odds ratios difficult, but the odds ratios for dogs and cats were more consistent. CONCLUSION: S. japonicum is endemic in areas of the Philippines despite implementation of control programmes. This may be due to the association of infections in dogs and cats with human infections. Infection control in dogs and cats is challenging, and there is a need to develop new methods to control transmission across all species