An Investigation of influenza type A, B outbreak in an Elderly Care Nursing Home, Mueang District, Lampang Province

Abstract

Background: Influenza remains a global public health concern, causing an estimated 290,000 to 650,000 deaths annually, with elderly individuals particularly vulnerable to complications such as pneumonia, reported in up to 58% of cases over the age of 65. On October 25th, 2024, a fatal case of influenza was reported in elderly care nursing home in Mueang District, Lampang Province, the outbreak investigation was performed to confirm the outbreak, describe its characteristics, identify the source, and implement control measures.

Methods: A retrospective cohort study was conducted from October 29th to 31st, 2024. Suspected cases were defined as residents or staff members presenting with fever and at least one of the following symptoms: cough, sore throat, rhinorrhea, fatigue, headache, or myalgia. Probable cases were those with a positive rapid influenza diagnostic test (RIDTs), while confirmed cases had RT-PCR confirmation of influenza virus infection. The investigation included environmental assessment, in-depth interviews with the index case and staff, and analysis of risk behaviors contributing to disease transmission.

Results: Of the 121 individuals in the elderly care nursing home (93 elderly residents and 28 staff members), 30 influenza cases were identified, with an attack rate of 24.8%. The median age of cases was 70 years (IQR 12.25 years). Among them, 8 were suspected cases, 8 were probable cases, and 14 were confirmed cases. The most common symptoms were fever and cough. Only two confirmed cases received oseltamivir; both infected staff members were unvaccinated, and the overall influenza vaccine coverage was 72.7%. RT-PCR results confirmed influenza A in 11 samples and influenza B in 3 samples. Elderly individuals were significantly more likely to be infected (aOR 9.39; 95% CI: 1.31–67.08), and increasing age was statistically associated with infection (p for trend = 0.015). The index case was a 70-year-old woman with underlying hypertension and diabetes who had not received the influenza vaccine. The first case was a food preparation staff member who rotated among multiple buildings and had inadequate hand hygiene, potentially acquiring the virus from a family member outside the facility. An environmental study revealed improper cleaning of high-touch surfaces such as handrails and doorknobs.

Conclusions: The outbreak likely stemmed from an infected food preparation staff member who introduced the virus from outside, spreading it within the nursing home. Key controls implemented included staff cohorting, enhanced hygiene, and promoting annual influenza vaccination to prevent future occurrences.