What’s the risk of nosocomial covid infection

The short version: the risk of catching COVID-19 in a hospital is real and measurable, but the exact number depends heavily on the ward, the patient, and the era.

The best direct evidence comes from a 2023 outbreak investigation on three unvaccinated cardiac wards [2]. Among 81 infections (42 healthcare workers and 39 patients), the attack rate for patients was 5.7%. The case fatality rate among those infected patients was 25.6% — 10 deaths out of 39 [2]. The strongest risk factor was spending more than half your time in a multi-bedded room, which tripled the odds of infection [2]. A 2024 genomic surveillance study across two hospitals found that about 45% of sequenced SARS-CoV-2 genomes formed transmission clusters, meaning in-hospital spread was common, with clusters lasting an average of 15 days [3].

The risk is not uniform. A 2021 study of leukemia patients found that stricter COVID-era precautions cut the rate of all nosocomial infections from 25.9 per 1,000 patient-days to 11.9 [1]. A 2022 study of double-occupancy rooms found a 16% attack rate among exposed patients [5]. A large English study attributed about 2.7% of all long-term care facility outbreaks to hospital seeding, but those seeded outbreaks accounted for 3.6% of all deaths in those facilities [4]. The risk is highest for patients with fluid/electrolyte disorders, neurological conditions, or those on immunosuppressants [2].

The evidence here is almost entirely from the pre-Omicron era, before widespread population immunity from infection or vaccination. It also focuses on hospitalized patients, not visitors or outpatients. The studies were not funded by vaccine manufacturers, which is a rare strength. The weakness is that most are outbreak investigations or observational cohorts, not randomized trials — you cannot randomize people to catch COVID in a hospital.

My call: the risk of nosocomial COVID-19 is substantial for hospitalized patients, especially in multi-bedded rooms, with attack rates in the range of 5-16% depending on the setting. The risk of death among those infected is serious, particularly for older or immunocompromised patients. Confidence: moderate.