HEP 444: Epidemiology

Dr. Adams

9/29/2022

HEP 444 Case Control Study Article

1. What is the rationale for performing the study?

There has been no investigation of the link between cardiovascular disease and exposure to outdoor air pollution in Lebanon. The paper’s focus is on exploring this connection among Lebanese adults and assessing whether or not cigarette smoking acts as a moderator.

2. What was the outcome variable in the study?

Cardiovascular diseases

3. Describe the cases

Individuals aged 40 and up who have been hospitalized for cardiovascular illness and who have been diagnosed by a cardiologist with ST elevation, non-ST elevation, myocardial infarction, stable/unstable angina, or heart failure.

4. Describe the controls

Adults aged 40 and over hospitalized to the same hospitals for any cause other than diabetes, hypertension, dyslipidemia, respiratory difficulties, or cardiovascular disorders served as the control group.

5. What were the two methods investigators used to obtain data?

• A face-to-face interview was completed by three independent investigators trained in a standardized manner.

• Questionnaires; The indication of transportation exposure to air pollution was evaluated by a series of questions.

6. What is the name of the risk statistic and measure of variability around the risk statistic used to determine a cause-effect relationship?

Continuous and categorical variables were described using means and 95% CIs, medians and interquartile ratios, and percentages, respectively.

7. Which characteristics between the cases and controls were not statistically different?

risk factors; hypertension, triglycerides, and LDL and Self-related global health

8. Which characteristics were more common in cases than controls (see text)?

Living in metropolitan regions, older age, and lower educational level were more prevalent in cases than controls.

9. Based on the OR (95% CI), which exposure to active and passive smoking had strength of association for the cases?

The odds ratio (OR) for CVD among current smokers was 1.92 (95% CI: 1.22–3.01), which was considerably greater than the risk among nonsmokers. Passive smoking was also associated with an increased risk (OR 2.35, 95% CI (1.46–3.78).

10. Based on the OR (95% CI), which exposure to outdoor air pollution did not have strength of association for the cases?

Living duration near highway between 1 to 14 years

11. Based on the OR (95% CI), which exposure(s) to outdoor air pollution showed dose response for the cases?

Highway proximity and Local diesel generator proximity

12. What is the percent increased risk of CVD living duration near a local diesel generator between 1 to 10 years and 11 years and more?

((31 - 29)/31) × 100 = 6%

13. What subject characteristics were adjusted for in the global model used to identify outdoor air exposures as a prior risk for CVD?

Handled the time spent residing close to a busy highway and the proximity to a nearby diesel generator as independent continuous factors rather than a dichotomous set.

14. Based on the highest adjusted odds ratios, what is the percent increase (compared to the referent value) of a case’s CVD events?

((5.04 -1.00)/ 1.00) × 100% = 80%

15. After stratifying the data by cigarette smoking status (nonsmoker, current smoker), what can you conclude about the effect of smoking on outdoor air pollution as an exposure for CVD events?

Smoking status was not observed to modify the link between proximity to a diesel generator and CVD (P for interaction: 0.24) in this study.

16. Identify how the authors explained (in the discussion or showed in the data) Hill’s criteria for causality.

Consistency of results

Death from cardiovascular causes was linked to proximity to a busy road in a five-year cohort study. Our findings further highlight the relevance of stratification by smoker status, since cigarette smoking moderates the connection.

17. Biological plausibility

Recent research employing rat macrophage cells assessed the cellular toxicity of PM in the city of Beirut (near busy highways and urban background sites). It shown that PM induced oxidative stress by causing an increase in reactive oxygen species (ROS). Numerous studies point to a biological link between air pollution chemicals with cardiac alterations.

18. Temporal relation

Regarding humans, a controlled exposure experiment to PM triggered both an acute and a long-lasting inflammatory response. In this case exposure preceded the outcome.

19. The investigators mentioned limitations that may have influenced the results of the study. How might “recall bias” influenced the results of the study?

It’s possible that the lack of knowledge on the part of the cardiologists who recruited the individuals about the subjects' exposure status reduced selection bias.

20. What did the investigators conclude about outdoor air pollution as a past risk factor for CVD?

In conclusion, the authors discovered that being exposed to outdoor air pollution, such as that from a nearby diesel generator or a busy highway, was linked to an increased risk of CVD. Dose-effect and time-relationship analyses also supported these findings.