Background: Inorganic arsenic is a lung, bladder, and skin carcinogen. One of th

Question

     Background: Inorganic arsenic is a lung, bladder, and skin carcinogen. One of the major sources of exposure to arsenic is through naturally contaminated drinking water. While positive associations have been observed between arsenic in drinking water and prostate cancer, few studies have explored this association in the United States. Objective: To evaluate the association between inorganic arsenic concentrations in community water systems and prostate cancer incidence in Illinois. Methods: Illinois Environmental Protection Agency data on arsenic concentrations in drinking water from community water systems throughout the state were linked with county-level prostate cancer incidence data from 2007 to 2011 from the Illinois State Cancer Registry. Incidence rates were indirectly standardized by age to calculate standardized incidence ratios (SIRs) for each county. A Poisson regression model was used to model the association between county-level SIRs and mean arsenic tertile (0.33-0.72, 0.73-1.60, and 1.61-16.23ppb), adjusting for potential confounders. Results: For counties with mean arsenic levels in the second tertile, the SIR was 1.05 (95% CI: 0.96-1.16). For counties with mean arsenic levels in the third tertile, the SIR was 1.10 (95% CI: 1.03-1.19). There was a significant linear dose-response relationship observed between mean arsenic levels and prostate cancer incidence (p for trend=0.003).

i.           What type of study design is this?

ii.         List the exposure and disease variables

iii.        What would you conclude from the results obtained in this study?

iv.        Can these results be generalized to individuals living in Illinois? Why or why not?

Explanation / Answer

i) It is an ecologic study

Ecological studies are the studies of factors which are risk-modifying factors on health based on geographically defined population.

ii) The exposure is to Arsenic levels and the disease variables are the occurrence of prostate cancer.

iii) The study show that the countries which have a high mean arsenic level in community water bodies have a significantly higher incidence of prostate cancer.

iv) Yes,

As the study was conducted in Illinois and samples and data are collected from Illinois, these results can be generalized to individuals living in Illinois.

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