Let's Mandate Masks

In May, a US citizen diagnosed with multidrug resistant tuberculosis (MDR TB) traveled to Europe, sparking a massive operation to identify the hundreds of airline passengers who he exposed to his illness. Fortunately, no secondary cases have been reported. Just two months later, a Taiwanese man, who also has MDR TB, and his wife, who has TB in the infectious phase, took Dragonair from Taiwan to Hong Kong and then to Nanjing, China, to attend a wedding. More than 270 passengers and crew were on the first flight, and more than 120 on the second.

Both passengers had been banned from traveling. These cases illustrate that voluntary compliance with travel restrictions does not always work.

TB is spread by coughing, which produces relatively heavy droplets that do not travel very far. Many of us have probably had the unpleasant experience of sitting near a passenger with a chronic cough during a long flight. Worse is the problem of a sneezer close by. Sneezing is due to irritation of the nasal mucosa by viruses, notably influenza viruses, which are expelled in microdroplets. Instead of quickly falling to the floor like TB droplets, these get caught up in the aircraft ventilation system and recirculated to the whole cabin. The longer the flight, the greater are the chances of spread.

What about long-distance travel by bus or train, or even commuter travel, where you may be holding a subway train strap with somebody coughing or sneezing in your face? At least there you can move, whereas on a packed flight it may not be possible to change your seat. What to do?

Well, everyone has probably seen those photos of New York or London during the 1918 flu pandemic, with everyone, including traffic police, wearing cloth masks. Nowadays we have more hygienic disposable paper ones. I think we should all carry masks with us for emergency use, either for protecting ourselves from others who are coughing or sneezing, or protecting others when we have a bout of the same, especially during the flu season. This could be particularly important to stop the spread of epidemic or bird flu. Westerners may feel self-conscious wearing masks in public, but the Chinese and Japanese have no such qualms. They can be seen all over their cities walking or cycling with white cloth patches covering the nose and mouth.

A University of Minnesota study found that even the least efficient mask tested had a filter efficiency (when optimally fitted) of more than 97% against particles averaging less than 1 micron in diameter - a category that includes the diseases mentioned above (Am J Infect Control, 22:65-74, 1994).

Influenza is transmitted by coughing, sneezing, or talking over a range of only three to six feet. TB bacteria, measles, and varicella (chickenpox) viruses can remain infectious over longer distances, infecting people in other rooms or plane cabins through the ventilation system. In both instances, masks should give good protection. When workers at the New York State TB diagnostic and research labs became infected with TB, the laboratory made masks mandatory, and the rate of infection plummeted.

The use of surgical masks is recommended in the pandemic influenza plans of the World Health Organization, the United States, and Canada. These masks cost around 15 cents (US) each. Simple cloth or paper surgical masks do not stop all viruses; that would require a beak-like N95 respirator and also eye goggles, as pathogens can get into the body from the surrounding mucosa. N95 respirators offer better protection, but at $1 to $3 each their use would be prohibitively expensive for nonhospital protection. These, of course, could be subsidized if need be.

In the meantime, if we all carried a few folded masks in our pocket or handbag, and used them whenever we have to spend hours in a crowded plane, bus, or train, and if airlines provided them free to coughing passengers and their neighbors, the spread of TB and airborne viral infections would be much reduced.

Jack Woodall is former director of the Nucleus for the Investigation of Emerging Infectious Diseases in the Institute of Medical Biochemistry at Brazil's Federal University of Rio de Janeiro.