Flu: surgical mask protects as well as expensive kN95 respirator

Pittsburgh - Disposable breathing masks that filter at least 95% of all aerosols from the air (kn95 mask with valve for sale) did not show health care workers more frequently from respiratory illnesses including one in the cold season in a randomized pragmatic study in the US medical journal (JAMA 2019; 322: 824-833) Proven flu protected as simple surgical face masks.

Surgical face masks filter the breathing air from doctors and nursing staff and thereby prevent infection of the patient. They are not actually intended for protection in the other direction, since the masks do not close completely on the facial skin. In addition, the masks are often worn "casually". Aerosols containing viruses or other pathogens can enter the respiratory tract by the side of the mask.

The US Centers for Disease Control and Prevention (CDC) therefore urgently advised staff during the 2009 H1N1 epidemic ("swine flu") to protect themselves from infection with KN95 respirators. Afterwards, they became standard respiratory protection in many US clinics. This not only puts a strain on the clinic's budget, since the KN95 respirators are relatively expensive. Due to their low wearing comfort, they are unpopular with the staff.

An earlier laboratory study on dummies had shown that the surgical face masks are better than their reputation if the masks are completely on the skin: 94.5% of viruses were found in a test series in Clinical Infectious Diseases (2012; 54: 1569-77) held back. The difference to the KN95 mask, which held back 99.8% of the viruses, was not very big. If the masks were only applied “loosely”, they held back less than 70% of the viruses. The KN95 respirator mask was also no more effective if it was not put on properly.

So there were legitimate doubts as to whether the KN95 respirators really achieve a greater protective effect in everyday clinical practice than a simple surgical face mask. A randomized study carried out by the CDC at seven centers now confirms this impression.

In 380 outpatient facilities, including polyclinics, dental surgeries, emergency centers, hemodialysis centers, emergency rooms and emergency services, staff were asked over four years during the flu season to wear either disposable KN95-certified respirators or conventional surgical face masks during patient contact.

The participants, 2,862 doctors, nurses or other personnel in contact with patients, were asked to report on an illness. In this case, a smear from the nose and throat was examined for pathogens. The primary endpoint was the frequency of confirmed influenza A or B virus infection.

According to a team led by Lewis Radonovich from a CDC laboratory in Pittsburgh, there were a total of 400 confirmed flu infections. Of these, 207 infections were attributable to the staff who were asked to wear KN95 respirators and 193 to the control group to use surgical face masks.

The difference between the two groups was therefore small and the adjusted odds ratio of 1.18, which even indicated a tendency advantage of the 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 (in which the worker may not have felt sick) in the groups with KN95 respirators, compared with 3,039 such events among those wearing surgical Face masks. The differences were not significant here either.

In the group with KN95 respiratory masks, 89.4% of the participants stated that they wore the masks “always” or “sometimes”. In the group with surgical face masks it was 90.2%. Refraining from the uncomfortable KN95 respirator is therefore not an explanation for the lack of superiority. For Radonovich, there is no overall reason why staff should be advised to buy the more expensive KN95 respirators during the flu season.