HLTH 6483 Module 2 Health Disparity Analysis Example

Nine Times the Rate on the Water: Measuring Disparities in Vibriosis by Sex, Age, Occupation and Liver Disease in a Gulf Coast County

Student Name

American College of Education

HLTH6483: Principles of Public Health and Epidemiology

Module 2 Assignment

Instructor Name

September 21, 2026

Introduction

Module 1 described 142 reported cases of vibriosis over ten years in a composite county on the Mississippi Sound, population about 210,000. The cases were concentrated among men, older adults, people who work on or near the water and people with chronic conditions, and all deaths were from Vibrio vulnificus. This paper measures those differences. It calculates rate ratios and rate differences for sex, age and water-related work, estimates how much of the county's burden falls on workers exposed through their jobs and compares case fatality among V. vulnificus patients with and without underlying conditions. It then asks which of these differences are health disparities in the sense that matters for equity and what drives them.

Disparity or Difference?

Some group differences are not disparities in the equity sense. Braveman (2006) defines health disparities as a particular kind of difference: systematic, plausibly avoidable differences in health that adversely affect groups who are already socially disadvantaged. A higher rate among men may reflect biology or voluntary exposure as much as disadvantage; a higher rate among low-wage workers who must handle raw seafood and work in contaminated water to earn a living fits the definition more closely. Measuring the size of each difference is the first step; deciding which ones are unjust is the second, and it requires evidence about why the difference exists.

Measures Used

Four measures are used. The rate ratio divides the rate in one group by the rate in a comparison group and shows relative difference. The rate difference subtracts one rate from the other and shows absolute difference, which matters for planning because it indicates how many cases would be avoided if the higher rate fell to the lower. The population attributable fraction estimates what fraction of the population's cases is associated with an exposure, assuming a causal link. The case-fatality ratio compares the proportion of cases who died in two groups. Rates are average annual rates per 100,000 over the ten years, using midpoint population estimates for each group.

Sex

Men accounted for 101 cases and women for 41. With about 102,000 men and 108,000 women in the county, the average annual rate was 9.9 per 100,000 among men and 3.8 among women, a rate ratio of 2.6 and a rate difference of 6.1 cases per 100,000 per year. The difference is consistent with men's greater participation in fishing, crabbing and water work, with higher rates of liver disease among men and with evidence that estrogen may offer women some protection against the most severe V. vulnificus illness (Oliver, 2005). Part of this difference is likely biological and part reflects exposure, and national surveillance likewise found most patients to be men (Newton et al., 2012).

Age

Residents aged 50 and older accounted for 97 cases, with about 84,000 people in that age group, and those under 50 for 45 cases among about 126,000. The average annual rates were 11.5 and 3.6 per 100,000, a rate ratio of 3.2. Age brings more chronic disease, weaker immune defense and, in this county, more time spent fishing in retirement. The age disparity matters for prevention because older adults are also the group most likely to die if infected with V. vulnificus.

Water-Related Work

The sharpest difference is occupational. About 6,500 county residents work in commercial fishing, oyster and crab processing, charter boats and marinas. They accounted for 34 cases, an average annual rate of 52.3 per 100,000, compared with 5.3 among all other residents, a rate ratio of about 9.9. Using Levin's formula with an exposure prevalence of 3.1% and that rate ratio, the population attributable fraction is about 21%: roughly one in five of the county's cases is associated with water-related work, even though these workers are only one in thirty residents. Many are paid by the catch or by the pound, work without paid sick leave and delay care for wounds. A substantial share are Vietnamese American fishers and processing workers with limited English, for whom health messages in English do not reach.

Underlying Conditions and Death

Among the 44 V. vulnificus cases, 21 had a recorded condition such as liver disease, diabetes, alcohol misuse or a weakened immune system, and 23 did not. Nine of the 21, or 43%, died, compared with 2 of the 23, or 9%, a case-fatality ratio of about 4.9. This pattern matches the clinical literature, which describes severe V. vulnificus infections occurring mostly in people with conditions that impair immunity or raise serum iron (Oliver, 2005). Liver disease in the county is itself unequally distributed, higher among men, among people with low incomes and among people with alcohol use disorder, so this biological vulnerability overlaps with social disadvantage.

Interpreting the Disparities

Measured by rate ratios, the largest disparity is occupational, followed by age and sex. Measured by rate differences, the occupational gap also dominates, at 47 cases per 100,000 per year. Measured by consequences, the gap in case fatality by underlying condition is the most lethal. Applying the definition from Braveman (2006), the occupational disparity is the clearest health disparity in the equity sense: it is systematic, largely avoidable through safer work practices and prompt care and falls on workers who are disadvantaged by pay, insurance and language. The disparity by liver disease is also partly social, while the difference by sex is more mixed.

What Would Narrow the Gaps

The measures point toward different remedies for different gaps. The occupational disparity calls for workplace measures: gloves and protective clothing for processing workers, first aid kits and wound care training on boats and at docks, paid time to seek care for an infected cut and messages delivered in Vietnamese and Spanish through the fishing cooperatives and churches that workers trust. The disparity by underlying condition calls for clinical action: physicians who treat people with liver disease, diabetes or immune suppression should warn them each spring against raw oysters and against exposing wounds to warm seawater, and emergency departments should suspect Vibrio promptly in these patients. The age disparity overlaps with both. The sex difference is least amenable to targeted action beyond the measures already listed. Each remedy can be judged later by whether it reduces the rate difference, the measure that shows how many cases the county could avoid.

Limits of the Measures

The measures rest on small numbers, and rates for subgroups, especially water workers, have wide uncertainty. Occupation is recorded only when patients report it, so the occupational count may be low, while the denominator for water workers comes from employment estimates that miss informal work. The population attributable fraction assumes that water work causes the excess risk and that no confounding factor, such as age, explains it; water workers in the county are younger than average, which would if anything make the true occupational effect larger. Underlying conditions are missing for a quarter of cases. National rates are not broken down in these ways, so comparison is limited.

Conclusion

Vibriosis in this county falls unequally. Men have about 2.6 times the rate of women, older adults about 3.2 times the rate of younger adults and water workers nearly ten times the rate of other residents, and V. vulnificus patients with underlying conditions die at roughly five times the rate of those without. The occupational disparity is the most clearly unjust and, because a fifth of cases are associated with it, among the most important for prevention. Module 3 turns to an outbreak investigation to see how these risks play out when many people are exposed at once.

References

Braveman, P. (2006). Health disparities and health equity: Concepts and measurement. Annual Review of Public Health, 27, 167-194. https://doi.org/10.1146/annurev.publhealth.27.021405.102103

Newton, A., Kendall, M., Vugia, D. J., Henao, O. L., & Mahon, B. E. (2012). Increasing rates of vibriosis in the United States, 1996-2010: Review of surveillance data from 2 systems. Clinical Infectious Diseases, 54(Suppl. 5), S391-S395. https://doi.org/10.1093/cid/cis243

Oliver, J. D. (2005). Wound infections caused by Vibrio vulnificus and other marine bacteria. Epidemiology and Infection, 133(3), 383-391. https://doi.org/10.1017/S0950268805003894