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limit spread of respiratory infection may have been aimed at limiting spread of tuberculosis, the general message remains relevant and appropriate today because of shared mechanisms of transmission for many respiratory infections.

Endangers You: Discover the Unknown Spreaders! National Tuberculosis Association, United States, ca.
1940. A father reads the newspaper in his armchair as his happy family gathers round — oblivious to the dangers
of contagious tuberculosis.Posters developed to support tuberculosis control advocate use of x-rays to discover unknown spreaders of infection. One poster shows a healthy-appearing middle class family – suggesting that anyone could be infected with tuberculosis. In the middle part of the 20th century (especially during the1940s and 1950s) mass chest x-ray screening programs were established in many cities, some employing specially equipped vans that toured the cities offering free chest imaging. Unfortunately, some screening programs used photofluorograms, photograms of fluoroscope images, rather than conventional x-rays. Apparently, many machines had no filters and no shielding, so screened individuals ended up receiving large doses of radiation. Although these mass screening programs detected some cases of unrecognized tuberculosis (some studies suggested that early programs detected about 20% of all cases of active tuberculosis), they also delivered radiation and its risks, which were not fully appreciated at the time. As the incidence of tuberculosis dropped, the yield from mass screening of the general population dropped and the approach was discontinued. Now routine screening x-rays are used only in selected populations with high risk of tuberculosis, such as prison populations in some cities or immigrants to the US coming from countries with a high incidence of tuberculosis.

Some posters speak to the dangers from drinking unclean water at a time when many in the U.S. had come to take safe drinking water for granted. One poster, dating from 1944, suggests the risk of death from drinking unclean water in a jungle stream and advises the soldier to drink only approved water. By this time in the U.S., many municipal water systems had come to rely on filtration and disinfection to virtually eliminate waterborne infections like typhoid fever and hepatitis A. It is a sad commentary that safe drinking water remains unavailable decades later to about a billion persons globally, and waterborne infections continue to claim lives, especially in developing countries.

Mary Elizabeth Wilson, MD
Associate Clinical Professor of Medicine, Harvard Medical School
Associate Professor of Population and International Health
Harvard School of Public Health