Investigation of a Coronavirus Disease 2019 (COVID-19) Outbreak at a Clinical Medical Education Center in Phuket Province, May 2025

Abstract

Background: COVID-19, caused by SARS-CoV-2, spreads mainly by respiratory droplets. Most infected individuals present with respiratory symptoms, though some remain asymptomatic. On 8 May 2025, 19 cases were reported among students and staff of a medical education center (MEC) in Phuket Province. The disease prevention and control and epidemiology unit collaborated with relevant agencies to conduct an outbreak investigation and implement control measures. The objectives were to confirm the outbreak, describe its distribution, analyze risk factors, and propose preventive actions.

Methods: This was a retrospective cohort study involving medical personnel and students, conducted between April 19 and June 2, 2025. We reviewed patients’ data from January 1 to May 3, 2025. Identify additional cases by screening and interviewing all individuals according to the case definitions: Suspected cases were defined as individuals who participated in the MEC freshman orientation activities and presented with clinical symptoms. Probable cases referred to symptomatic individuals with a positive antigen test kit (ATK) result. Confirmed cases were defined as those with via reverse transcriptase polymerase chain reaction (RT-PCR) or a positive whole genome sequencing (WGS) result. Asymptomatic case was defined as any individual with a positive ATK or RT-PCR result. Data on risk behaviors were collected to analyze the association between risk factors and COVID-19 infection using univariable and multiple logistic regression, and presenting the relative risk, adjusted odds ratio, 95% confidence interval, and p-value. We also conducted an environmental study and applied the 7-1-7 metrics to assess the timeliness of system performance.

Results: Of 108 participants, 55 cases were identified: 11 suspected, 32 probable, 10 confirmed, and 2 asymptomatic (attack rate 50.9%). The majority of cases were among fifth-year medical students (16 cases, 66.67%) and center staff (8 cases, 66.67%). The median age was 23 years (range 21–59 years). While 96.36% of patients were symptomatic, there were no cases of pneumonia or hospitalization. The circulating viral strains identified were Omicron B.1.1.529 sublineage XEC and NB.1.8.1. The outbreak pattern was a propagated source. Significant risk factors included participating in "getting-to-know-you" walking activities, traveling together in an air-conditioned van, sharing meals, and attending the briefing session led by the medical lecturer. The response process achieved detection within 2 days, notification within 3 days, and initial control within 6 days according to the 7-1-7 metrics.

Conclusion: This event represents a COVID-19 outbreak associated with an orientation activity at a MEC in Phuket Province. The transmission was linked to group activities in enclosed spaces. Therefore, continuous emphasis must be placed on prevention measures following the D-M-H-T guidelines (Distancing, Mask-wearing, Handwashing, Testing), timely case reporting, and intensive surveillance in high-risk areas to mitigate further spread.