Epidemiological investigation on an outbreak of food-borne disease caused by nitrite poisoning

Sodium nitrite, often mistaken for common table salt or sugar due to its similar appearance, has resulted in poisoning incidents. This report details a cluster of sodium nitrite poisoning stemming from a dinner gathering on a maintenance ship. The epidemiological investigation aims to uncover the incident's cause, provide clinical insights, and offer preventive recommendations for similar events in the future. Individual interviews were conducted with all suspected cases, capturing basic information, clinical symptoms and onset times, dining history, and food exposure. Gathering organizer and food preparer was interviewed to gather potential leads regarding the poisoning incident. Blood samples from cases were collected for methemoglobin testing, and samples of vomit, leftovers, and the dining environment were collected for sodium nitrite detection. A total of 11 people participated in the dinner party, and 6 of them developed symptoms, with an attack rate of 54.55%. Clinical presentations mainly included dizziness, weakness, nausea, vomiting, and cyanosis of the lips, with elevated methemoglobin levels. The shortest incubation period was 0.5 hours, the longest was 3 hours, with a median of 2 hours. All cases showed rapid symptom relief after treatment with the specific antidote methylene blue. A retrospective cohort study showed that the incidence rate among those who consumed vegetable and tofu soup was 85.71% (6/7), which was higher than that of nonconsumers (0/4), and the difference was statistically significant (relative risk = 7.000, 95% confidence interval = 1.140-42.969). Sodium nitrite concentrations in vomit samples ranged from 5.40 to 37.17 mg/kg, while leftovers showed levels of 170.88 mg/kg in a vegetable and tofu soup, 55.65 mg/kg in goose meat, and 9.17 mg/kg in other leftovers. Furthermore, environmental samples from the suspected condiment storage area tested positive for sodium nitrite. This cluster of sodium nitrite poisoning was due to the inadvertent use of sodium nitrite in cooking, mistaken for table salt. Public awareness campaigns on food safety should be intensified across multiple platforms, and enhanced oversight of nitrite usage is crucial to prevent similar poisoning incidents.