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Deadliest Outbreaks: Oregon’s 1922 Raw Milk Epidemic

Editor’s Note: Four of the 10 deadliest outbreaks of foodborne illness in the United States occurred during the first half of the 20th century. In a periodic, four-part series beginning today, Food Safety News explores the fifth deadliest outbreak, which occurred in Portland, OR in 1922. Streptococcus linked to unpasteurized milk killed 22 and sickened 487.

On March 25, 1922, a two-year-old Portland child “with the clinical picture of sore throat and acute encephalitis” died. Over the next days, nearly 500 people would be infected and 21 more children would die in an outbreak of foodborne disease that was both quick and deadly.

Three days after that first death, Portland’s city health bureau turned to the University of Oregon’s Medical School for help, eventually authorizing medical Dr. R.L. Benson and H.J. Sears, who had a Ph.D in bacteriology, to “undertake an investigation.”

Benson and Sears not only conducted a most thorough investigation, but also recorded their findings in an 11-page report published in the June 2, 1923 edition of the Journal of the American Medical Association.

“A Milk-Borne Epidemic of Septic Sore Throat in Portland, Oregon” by Benson and Sears tells how their investigation led them to “a single raw milk dairy.” In many ways, their report was as detailed as those done today by the federal Centers for Disease Control and Prevention  (CDC).  

The Benson-Sears report even includes a level of detail not found in CDC public reports — Table 2 is a log of all 22 of the deaths, including the case number, gender, age, date of death, onset of illness date, and notes on contributing causes in the 1922 outbreak.

Benson and Sears did not run a passive investigation.  “On our recommendation, the health bureau at once ordered heating of all of the (raw) milk of this dairy by whatever method would be feasible, and placed two employees of the bureau in charge of the dairy,” they wrote.

Within 24 hours, after milk from the dairy was heated, the incidence of new cases of septic sore throat in the community dramatically declined, Benson and Sears reported.

Once the infections were halted, Benson and Sears turned their attention to the raw milk dairy, where they found 51 “milking cows of various breeds housed in a wooden structure with concrete floors and with proper facilities for flushing floors and handling excreta.”

Benson and Sears found the system for cooling milk was efficient. But “we learned that cows having diseased udders were kept in their regular stalls along with healthy cows, and in some instances only the diseased quarter was excluded from milking,” they reported. Benson and Sears concluded it might not always be possible for whomever milked a cow to know which milk should be discarded, because different cows were milked on different shifts.

“Except for the points mentioned, we found the sanitary conditions generally good and city milk inspection had always given this dairy one of the best ratings in the city as regarded bacterial count and general quality of milk,” they said.

Cultures of milk from the herd taken on March 28, 1922 “gave very few hemolytic streptococcus colonies.” But the dairyman said milk from cows with diseased udders had been excluded.  When Benson and Sears examined diseased cows, they focused their attention on one dubbed Cow 51.  It had a “consolidation” of the left front quarter of the udder.

The dairy farmer claimed milk from Cow 51 had not reached consumers for the past two weeks.  After letting milk from this cow stand for 24 hours, the investigators noted it “settled out” differently, and consisted of “yellowish, creamy pus.”  A culture revealed 10,000,000 hemolytic streptococci per cubic centimeter from the diseased quarter of the udder.

Benson and Sears concluded that Cow 51 was “the probable source of the epidemic.”  They said the animal’s milk was likely included in “the herd milk unknown to the operator of the dairy.”  They figured the herd milk became infected on March 22 and the contamination continued for a day or two after.  

The culture from the herd resembled the organism found in the human cases of septic sore throat.

At the time of the epidemic, at least 1,400 Portland residents were getting their milk and cream from the dairy.  About one out of three — 487 — became infected, suffering from large red inflamed tonsils and sore throats. According to Benson and Sears, 166 of these cases were severe with “protracted sepsis.”  Another 321 cases were moderate or mild.

Two Portland institutions were especially hard hit in the 1922 outbreak.

Of 69 patients and staff at a local hospital when the outbreak occurred, 23 got the septic sore throat and three died. At a home for girls, 45 of the 104 milk drinkers were infected, but fortunately none of those illnesses was fatal.

Other victims of the outbreak lived in private homes, mostly on Portland’s west side.

© Food Safety News