How effective are surgical masks

Influenza: Surgical mask protects just as well as expensive N95 respirator

Pittsburgh - Disposable breathing masks, which filter at least 95% of all aerosols from the air (N95), have in a randomized pragmatic study in the American medical journal (JAMA 2019; 322: 824-833) did not protect health workers from respiratory illnesses, including known flu, more often than simple surgical face masks during the cold season.

Surgical face masks filter the air breathed by doctors and nurses, thereby preventing the patient from becoming infected. They are not actually intended for protection in the other direction, as the masks do not close completely to the skin of the face. In addition, the masks are often worn "casually". Aerosols containing viruses or other germs can penetrate the side of the mask into the airways.

The US Centers for Disease Control and Prevention (CDC) therefore urgently advised staff during the H1N1 epidemic of 2009 (“swine flu”) to protect themselves from infection with N95 respirators. In many US clinics, they have then become the standard respiratory protection. This not only puts a strain on the clinic's budget, as the N95 respirators are relatively expensive. Due to their low wearing comfort, they are unpopular with staff.

An earlier laboratory study on dummies had shown that the surgical face masks are better than their reputation when the masks lie completely on the skin: Viruses were found in a test series in Clinical Infectious Diseases (2012; 54: 1569-77) to 94.5% held back. The difference to the N95 respirator, which held back 99.8% of the viruses, was not very big. If the masks were only put on "loosely", they held back less than 70% of the viruses. The N95 respirator was also not more effective if it was not put on properly.

So there were justified doubts as to whether the N95 respirators really achieve a greater protective effect in everyday clinical practice than a simple surgical face mask. A randomized study that the CDC carried out at seven centers has now confirmed this impression.

In 380 outpatient facilities, including polyclinics, dental practices, emergency centers, hemodialysis centers, emergency rooms and rescue services, staff were asked for four years during the flu season to wear either N95-certified disposable respirators or conventional surgical face masks when they came into contact with patients.

The participants, 2,862 doctors, nurses or other staff with patient contact, were asked to report if they became ill. In this case, a swab from the nose and throat was examined for pathogens. The primary endpoint was the frequency of confirmed infection with influenza A or B viruses.

As a team led by Lewis Radonovich reports from a CDC laboratory in Pittsburgh, there were a total of 400 confirmed flu infections. Of these, 207 infections were attributable to staff who were asked to wear N95 respirators and 193 to the control group who were supposed to use surgical face masks.

The difference between the two groups was therefore small and the adjusted odds ratio of 1.18, which even showed a tendency towards the advantage of surgical face masks, was not significant with a 95% confidence interval of 0.95 to 1.45.

In addition, there were 2,734 illnesses with flu-like symptoms or laboratory-confirmed respiratory illnesses or acute or laboratory-proven respiratory infections (where the worker may not have felt ill) in the groups wearing N95 respirators, compared to 3,039 such incidents in the wearers of surgical procedures Face masks. Here, too, the differences were not significant.

In the group with N95 respirators, 89.4% of the participants stated that they "always" or "sometimes" wear the masks. In the group with surgical face masks, it was 90.2%. Doing without the uncomfortable N95 respirator is therefore out of the question as an explanation for the lack of superiority. Overall, for Radonovich, there is no reason why staff should be advised to use the more expensive N95 respirators during the flu season. © rme / aerzteblatt.de