Pneumonic plague.

The primary pneumonic plague outbreaks in Oakland in 1919 and Los Angeles in 1924 constitute good points of reference for epidemiological observations and experimental studies on this form of plague. Retrospective analysis of them reveals some still unanswered questions. In the Oakland outbreak (24), a man went hunting in the hills of Contra Costa County in April 1919 and perhaps took home a squirrel for food. He fell ill about 4 days later, having an axillary bubo and a secondary pneumonia. Another man living in the same house contracted plague and in turn passed it directly or indirectly to 12 others. All of the patients died, plus two physicians and two nurses. Confusing clinical and bacteriological observations raise some doubt that plague was the cause of death of one of the nurses. The disease was first taken to be influenza, but the diagnosis was changed after bipolar bacilli were seen in smears from the lung and after animal inoculation tests in one case. Plague was not found among 6,000 rats trapped soon afterward, but infected squirrels were discovered in the area where the man had hunted. The weather was warm and dry. As reported on the Los Angeles outbreak (9), in October 1924 a Mexican woman died after an illness of 4 days. Her husband and nurse became ill and both died. The cause of death of the husband was given as "double lobar pneumonia." Within 2 days, 32 cases of pneumonic plague, all fatal, were discovered in persons living in the house and in friends and relatives who had visited the home of the first patient, who probably had had a secondary plague pneumonia. Among them were four children 10 years old or less, one woman of 50, a priest, a nurse, and an ambulance driver who helped transport the patients. Bubonic plague had been diagnosed in other patients in the area, and plague bacilli were found in commensal rats that had in all probability contracted it from squirrel fleas. The climate was not unusual. The clinical histories, autopsy reports, and cultures of the plague strains isolated from ten of the victims did not indicate where the first patient contracted the infection nor precisely how it spread. Similar epidemics had been observed in India (50) and in Manchuria in 1910-1911 and 19201921. According to the classical account of Sticker (56, 57), pneumonic plague was first seen to be associated with bubonic plague in the 14th century. In few accounts is it clear whether the pneumonia was primary or secondary and to what extent it was contagious. By the middle of the 16th century it was noticed that pneumonic outbreaks were preceded by bubo pest. From the earliest time the question of how plague spreads has been the foremost one. At first this was a very simple question, and for lack of specific information the principle of isolation was applied if possible. So far as the pneumonic form is concerned, the question remains largely unanswered even though many empty spaces in general knowledge of plague and its spread, especially the bubonic form, have been filled. In a valuable collection of letters at the University in Basel, Switzerland, between the humanists and Paracelsists dealing with plague in 15631564, a significant, simple, still tenable concept of spread is spelled out (23). J. Crato, in a letter dated 1565 and addressed to Theodor Zwinger, wrote that transmission of pneumonic plague is due to inhalation of plague seminaria in the expired air of plague patients who exhale the plague contagium and disperse it in the air. The significance of the concept, that pneumonic plague is airborne, was not realized because in the depopulating epidemics that gave it the name of Black Death, pneumonia was subordinate in the spread of plague in Europe. Procedures to test this concept became available only during the most recent pandemic and the great Manchurian pneumonic plague epidemics of 1910-1911 with 60,000 deaths. Their extreme infectivity under climatic and living conditions favorable to spread are well documented (68). The pneumonic form was first bacteriologically proved by Childe (6) in cases in Bombay in 1896. Strong and Teague (58) and Strong, Crowell,