Nonthermal plasma air purification reduces infection rate and alleviates symptoms in upper respiratory tract infections: A randomized controlled trial

As most of our time is spent indoors, indoor air quality is crucial, especially during seasonal virus outbreaks. Acute upper respiratory tract infections (URTIs) are among the most prevalent diseases globally, leading to symptoms like coughing, nasal congestion, and fatigue, along with significant healthcare costs. Since aerosols play a key role in infection transmission, improving indoor air quality is essential. Nonthermal plasma (NTP) has shown promise in inactivating airborne microorganisms, offering a potential solution for antiviral air purification without the need for filters. The AirDisP_URTI study investigated whether NTP air germ inactivation in real-world office settings could reduce URTI incidence over a 5-month period. Initially, the NTP air purifier’s effectiveness was tested in a laboratory. This was followed by an intervention study that measured infection events and severity using the WURSS-21 questionnaire, health checks, saliva samples, and an aerobic endurance test. A total of 230 participants were randomized, with 150 included in the final analysis: 73 in the NTP group and 77 in the control group. The NTP group experienced noticeably milder symptoms compared to controls. Statistically, symptom severity was significantly reduced (p = 0.028). Based on infection counts - 24 in the NTP group and 32 in the control group - the odds of infection were higher in the control group, with an OR of 1.45 (95% CI: 0.75-2.78), indicating a 45% increased risk of infection without the NTP air purifier. The absolute risk reduction (ARR) was 8.68%, favoring the NTP group. Molecular analysis of saliva revealed lower levels of salivary immunoglobulin A and C-reactive protein in the NTP group, supporting a milder disease course; IgA differences were statistically significant (p = 0.039). These findings suggest that NTP air purifiers can reduce the incidence and severity of URTIs, though larger studies are needed to confirm broader impacts. Trial Registration: ISRCTN identifier: ISRCTN11050992.