Hand Sanitizer May Not be Entirely Effective Against the Flu

The influenza A virus (IAV) remains contagious in wet mucus from infected patients, even after being exposed to an ethanol-based disinfectant (EBD) for 2 full minutes, according to researchers at Kyoto Profectural University of Medicine, in Japan. Fully deactivating the virus, they found, required nearly 4 minutes of exposure to EBD.

The researchers found that the thick consistency hydrogel structure of mucus keeps the ethanol from reaching and deactivating the IAV and protects the virus from deactivation. Until the mucus has completely dried, infectious IAV can remain on the hands and fingers, even after appropriate antiseptic hand rubbing.

The study first found that ethanol spreads more slowly through the viscous substance than it does through saline after researchers first studied the physical properties of mucus. Then, in a clinical component, the researchers analyzed mucus that had been collected from IAV-infected patients and dabbed on human fingers simulate situations in which medical staff may transmit the virus. After 2 minutes of exposure to EBD, the IAV virus remained active in the mucus on the fingertips. By 4 minutes, however, the virus had been deactivated.

This current study challenges previously established findings that suggest ethanol-based disinfectants are effective against IAV. According to the study authors, most studies on EBDs test the disinfectants on mucus that has already dried, since when the researchers used fully dried mucus, they found that hand rubbing inactivated the virus within seconds. In addition, the fingertip test used may not exactly replicate the effects of hand rubbing, which through convection might be more effective at spreading EBD.

For flu prevention, both the CDC and the WHO recommend hand hygiene practices that include using EBDs for 15 to 30 seconds. However, that's not enough rubbing to prevent IAV transmission, according to the study.

Although the current sanitizing efforts were ineffective, the study found that washing hands was more effective than simply rubbing. Washing hands with an antiseptic soap, they found, deactivated the virus within 30 seconds, regardless of whether the mucus remained wet or had dried.

Reference

• Towards Better Hand Hygiene for Flu Prevention [press release]. American Society for Microbiology website. https://www.asm.org/Press-Releases/2019/September-1/Towards-Better-Hand-Hygiene-for-Flu-Prevention. Published September 18, 2019. Accessed September 23, 2019.
• Ryohei Hirose, Takaaki Nakaya, Yuji Naito, Tomo Daidoji, Risa Bandou, Ken Inoue, Osamu Dohi, Naohisa Yoshida, Hideyuki Konishi, Yoshito Itoh. Situations Leading to Reduced Effectiveness of Current Hand Hygiene against Infectious Mucus from Influenza Virus-Infected Patients. mSphere, 2019; 4 (5) DOI: 10.1128/mSphere.00474-19