The NC State Health Director charged your team to investigate the health effects of a GenX chemical spill from the Chemours chemical plant into the lower Cape Fear river basin.

The NC State Health Director charged your team to investigate the health effects of a GenX chemical spill from the Chemours chemical plant into the lower Cape Fear river basin.  GenX (perfluoro-2-propoxypropanoic acid) is part of a large chemical class of per- and polyfluoroalkyl substances (PFAS) and is used to make Teflon.  While PFOA and PFAS have been studied, less is known about GenX health effects. You completed your analysis on the cohort study, in which you examined the potential relationship between GenX exposures in drinking water and elevated liver enzymes. On going water monitoring indicates exposures above the 140 ng/L cutpoint as recently as last year. 

Your initial findings of an association between GenX exposure and increased risk of elevated liver enzymes (Exam 1) generated substantial interest from the NC State Health Director, their staff, and people living in Wilmington and along the Cape Fear River. 

You’ve now been asked to conduct a case control study of liver cancer and GenX exposure. You and your team were awarded a NC Division of Public Health contract to review the literature, conduct analyze a case control study, and interpret your results.  You used the North Carolina Central Cancer Registry to locate 51 people with newly diagnosed liver cancer. You randomly selected and recruited 51 people from the North Carolina Department of Motor Vehicles registry to serve as controls.  Your colleagues have asked you to consider potential sources of systematic error.  Note this example is instructional, however, increased PFOS exposures have recently been reported to associated with increased odds of liver cancer, see Cao L, Guo Y, Chen Y, Hong J, Wu J, Hangbiao J. Per-/polyfluoroalkyl substance concentrations in human serum and their associations with liver cancer. Chemosphere. 2022 Jun;296:134083.

To better understand your data set, you examine whether water source is a potential EMM in the relationship between GenX  and liver cancer using stratification. Complete the table below. Estimates should be presented to two digits after the decimal. Use the exact 95CI% test, rather than Woolf.

Table 2. Crude and Water source Stratum-specific Odds Ratio between GenX Exposure and Liver Cancer  

Measure Estimate 95% CI

Crude OR

Stratum-specific OR

Surface water

Well water