HLTH 6483 Module 1 Epidemiological Data Analysis Example

Warm Water, Raw Oysters and Open Cuts: An Epidemiological Analysis of Rising Vibriosis in a Gulf Coast County, 2016 to 2025

Student Name

American College of Education

HLTH6483: Principles of Public Health and Epidemiology

Module 1 Assignment

Instructor Name

September 14, 2026

Introduction

Vibriosis is illness caused by Vibrio bacteria other than the toxigenic strains that cause cholera. The bacteria live naturally in warm, brackish coastal water and infect people who eat raw or undercooked shellfish or whose skin wounds are exposed to seawater. In a composite Mississippi Sound county home to roughly 210,000 people, where oyster bars, charter fishing and beach tourism drive the economy, the health department has noticed more reports each summer. This paper analyzes ten years of reported cases, 2016 through 2025, describing the disease by time, place and person, calculating rates and severity measures, comparing the county with national surveillance and assessing the limits of the data. It sets up the modules that follow, which examine disparities, an outbreak, a key study, a prevention program and a recommendation.

Data Sources

Vibriosis has been nationally notifiable since 2007, and cases are reported through state health departments to the Cholera and Other Vibrio Illness Surveillance system, known as COVIS. The county's data come from the state's notifiable disease system, which captures laboratory-confirmed cases with demographic information, dates of onset and a case report form covering seafood consumption, water exposure, underlying conditions and outcome. Population denominators come from annual county population estimates. National comparison figures come from a review of COVIS and the active Foodborne Diseases Active Surveillance Network, FoodNet, which found that reported vibriosis rose between 1996 and 2010 from 0.09 to 0.28 cases per 100,000 in COVIS and from 0.15 to 0.42 in FoodNet (Newton et al., 2012).

Time: A Rising Trend

The county recorded 142 cases over the ten years. Annual counts rose from 8 in 2016 to 21 in 2025, and the incidence rate rose from about 3.9 to 10.0 cases per 100,000 residents, well above national figures, as expected for a Gulf coast population with heavy water exposure. The trend is not perfectly smooth; counts dipped in 2020, when beaches and restaurants were closed for part of the season, and rose sharply in 2023 and 2025, both years with long periods of unusually warm coastal water. A simple linear fit suggests an increase of about 1.3 cases per year, although ten points are too few to separate a steady rise from a few hot years.

Time: Seasonality

Vibriosis is strongly seasonal. Of the 142 cases, 111, or 78%, had onset between May and October, peaking in July and August. National surveillance shows the same summer peak (Newton et al., 2012). Seasonality is consistent with the biology of Vibrio species, which multiply in water above roughly 20 degrees Celsius, and with human behavior, since swimming, fishing and raw oyster consumption also peak in summer. The winter cases, mostly linked to oysters eaten in restaurants, suggest that some risk continues year-round.

Place

Cases were concentrated among residents of the county's two coastal cities, which had rates about twice those of inland ZIP codes. About a fifth of cases were visitors reported by county hospitals but residing elsewhere; they are excluded from resident rates but matter for prevention, since tourists may not know local risks. Case report forms show that exposures clustered around the county's bays and bayous, where warmer, less salty water favors Vibrio vulnificus, rather than the open Gulf beaches.

Person

The typical case was an older man. Men made up 71% of cases, and the median age was 58 years. Among cases with information on underlying conditions, 46% reported liver disease, diabetes, heavy alcohol use or immune suppression. These patterns match the literature on Vibrio vulnificus, which describes severe infections occurring largely in men over 50 with conditions such as liver cirrhosis, chronic hepatitis or iron overload (Oliver, 2005). The county's data also show that 24% of cases worked on or near the water, including commercial fishers, oyster shuckers and charter crews.

Species and Route of Exposure

Vibrio parahaemolyticus accounted for 38% of cases, Vibrio vulnificus 31%, Vibrio alginolyticus 18% and other species 13%. Route of exposure differed by species. Most V. parahaemolyticus infections followed raw shellfish consumption and caused gastroenteritis. Most V. alginolyticus infections involved ear or wound infections after swimming. V. vulnificus infections were divided between raw oyster consumption, leading to bloodstream infection, and wound exposure, such as a cut while fishing or crabbing, leading to severe skin and soft tissue infection. Overall, 44% of cases reported seafood consumption as the likely exposure and 51% reported water or wound exposure.

Severity

Seventy-four patients, 52%, were hospitalized, and 11 died, a case-fatality proportion of 7.7% overall. All 11 deaths were among the 44 V. vulnificus cases, a case-fatality proportion of 25% for that species, and 9 of the 11 had liver disease or another listed condition. The county's burden is therefore two problems in one: a larger number of mostly mild infections from several species and a smaller number of devastating V. vulnificus infections concentrated among older men with chronic illness. Nationally, most hospitalizations and deaths in both surveillance systems were caused by V. vulnificus (Newton et al., 2012).

How the County Compares

Set beside national surveillance, the county's pattern is familiar in shape and larger in scale. Its species mix, summer peak, predominance of men and concentration of deaths among V. vulnificus cases all echo the national review (Newton et al., 2012). Its rates are many times higher, which reflects both greater exposure, since a larger share of residents work, fish and swim in warm brackish water, and possibly more complete reporting, because local clinicians see the disease often and order the right cultures. The county's upward trend also parallels the national rise, though the causes may differ in weight: national increases have been attributed in part to warming water and improved detection, while wound infections along the eastern seaboard have also spread northward over three decades (Archer et al., 2023), while the county's recent surge coincides with two unusually hot summers and a new oyster bar district that opened in 2022.

Questions the Data Raise

Descriptive epidemiology generates hypotheses rather than testing them, and this analysis raises several. Is the rising trend driven by warmer water, by more people eating raw oysters or by better testing? Are the high rates among older men explained by exposure, by underlying illness or by both? Why do inland residents with the same underlying conditions have lower rates, and is that difference about exposure or about reporting? Are workers on the water being infected through wounds at work, which would make vibriosis partly an occupational health problem? The remaining modules take up these questions by measuring disparities, examining an outbreak, critiquing a study that links infections to sea temperature, evaluating a regulatory program and making a recommendation.

What the Data Cannot Show

Reported cases understate the true burden, because many people with mild vibriosis never see a clinician, and those who do may not have a stool or wound culture processed on media that detect Vibrio. Reporting may also have improved over time as clinicians and laboratories became more aware, which could inflate the apparent trend. The case report form relies on patients' recall of exposures, and information on underlying conditions is missing for about a quarter of cases. Visitors complicate rates. With only 142 cases, subgroup rates are unstable, and single years can swing widely. These limits argue for caution in interpreting the trend but not for dismissing it, since national surveillance and the county's own data point in the same direction.

Conclusion

Vibriosis in this Gulf coast county is rising, strongly seasonal, concentrated in coastal communities and among older men with chronic conditions and divided between foodborne and wound infections. The most severe outcomes come from V. vulnificus. Module 2 will measure the disparities these patterns suggest, particularly by age, sex, occupation and health condition.

References

Archer, E. J., Baker-Austin, C., Osborn, T. J., Jones, N. R., Martínez-Urtaza, J., Trinanes, J., Oliver, J. D., González, F. J. C., & Lake, I. R. (2023). Climate warming and increasing Vibrio vulnificus infections in North America. Scientific Reports, 13, Article 3893. https://doi.org/10.1038/s41598-023-28247-2

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