Continuing Mystery

More cases of infantile paralysis were reported in the U.S. during 1949 than in any previous year. Last week the total passed 43,000. As the sad statistics piled up, officials of the U.S. Public Health Service combed through mountains of reports, noting where poliomyelitis had struck most heavily, hoping that locating the outbreaks would help to explain them. The results were discouraging.

A U.S. map was divided into two zones along a line running west from the southern boundary of Virginia (36DEG 30' N. Lat.) with 1,948 counties in the northern zone, 1,147 in the southern. Only 82 counties--distributed helter-skelter across the country in both zones--reported no polio cases between 1932 and 1946--the period under study. Of the 83 counties which had had epidemics, all but seven were within the northern zone. But within this zone, no clear pattern was apparent.

When counties were compared by population, some unexplained differences showed up. In both north & south, only the least populous counties reported no cases. But in the north, when epidemics struck, they appeared to hit thinly populated rural areas or small cities more often than jampacked big cities. In the south, the bigger the city the more polio.

Another team of statistics-minded doctors went to work on the worst 1948 epidemic within a single county--San Diego. The city of San Diego, they point out in the current Stanford Medical Bulletin, "probably has better living conditions than any large city in the U.S." Nearby is the overcrowded, jerry-built, almost sewerless Mexican town of Tijuana. Every racial group in San Diego, including Mexican immigrants, showed about the same liability to polio (60 cases per 100,000 population). But Tijuana's rate was only one-seventh as great.

A lot of old theories about polio came into question: there was no close relation between temperature peaks and polio peaks; crowd-begetting holidays and fairs did not seem to give the disease any extra encouragement. Three famed bugaboos--swimming, travel and over-exertion--seemed to precede the disease only in rare cases.

Though some communities in San Diego County showed a high polio rate among the people who came into contact with polio victims, others did not. Nonetheless, the doctors recommended more thorough isolation and quarantine. That was all they could offer. Otherwise, the old questions of how, when and where people catch polio remained a mystery.

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