In November 1982, 31 (8.8%) of 353 residents at a home for the aged in Ottawa, Ontario, Canada, became ill with gastrointestinal symptoms. Cases occurred over an 18-day period (Figure 1). Eight of the ill patients had loose stools only, while 18 of the 23 more severely ill patients had watery, bloody diarrhea. For those with loose stools only, illness lasted 1-2 days; for those more severely ill, illness lasted 5-12 days. Four patients were hospitalized, and one with metastatic uterine carcinoma died.

None of the usual enteric pathogens (Salmonella, Shigella, Campylobacter, Yersinia, or Amoeba) were found in stool specimens obtained from the 31 affected residents. Escherichia coli O157:H7 was isolated from the stools of 17 patients, with the isolation rate higher for those with watery, bloody diarrhea (78%) than for those with loose stools only (38%). In studies of serial stool specimens, E. coli O157:H7 was usually isolated from the time diarrhea began until formed stools returned, up to 11 days after onset.

Food prepared in the home's kitchen was a possible source of the outbreak. A single lot of hamburger had been served repeatedly between November 6 and 20 and was considered the most likely vehicle. Two samples of frozen meat from this lot were cultured, but E. coli O157:H7 was not recovered.

The cases beginning between November 8 and 16 occurred among residents of seven floors throughout the home's two buildings, whereas all three cases occurring after November 16 were from a single floor, where residents are mentally incompetent. These three individuals may have acquired infection through person-to-person transmission.

The National Enteric Reference Centre of the Canadian Laboratory Centre for Disease Control (LCDC) serotyped the E. coli from this outbreak. Further analysis at LCDC of the E. coli Ol57:H7 strains demonstrated that, although they did not produce heat-labile (LT) or heat-stable (ST) enterotoxin and were not invasive, they produced a cytotoxin in the Vero cell tissue culture assay (1); 80% of the isolates fermented sorbitol after 4-5 days.

Since 1978, LCDC has received six isolates of E. coli O157:H7 from sporadic cases of gastrointestinal illness. All five for which histories are available were from patients with hemorrhagic colitis. Reported by Canada Diseases Weekly Report 1983, 9:29-32; Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: This report of a third outbreak of hemorrhagic colitis associated with isolation of E. coli O157:H7 (2,3) further implicates this E. coli serotype as an important cause of hemorrhagic colitis syndrome. Isolation of the organism from patients with nonbloody diarrhea that occurred during the outbreak gives added evidence that E. coli O157:H7 can cause a spectrum of gastrointestinal illnesses. Although later cases among a group of patients with poor personal hygiene suggested that person-to-person transmission may have occurred, no evidence existed for this mode of transmission in the two previously described outbreaks (2).

The pathophysiology of hemorrhagic colitis is unknown. Documentation that E. coli O157:H7 produces a cytotoxin for Vero cells (1) suggests the organism may produce an enterotoxin distinct from LT and ST; however, further work is necessary to show that this cytotoxin plays a role in pathogenesis.

Since August 1982, 39 cases of sporadic hemorrhagic colitis have been reported to CDC from 18 states. E. coli O157:H7 has been isolated from six of 21 stool specimens submitted from these patients. These isolates ferment sorbitol slowly or not at all.

CDC is continuing to investigate sporadic cases of hemorrhagic colitis (3) and requests that cases with acute onset of symptoms fulfilling the following criteria: 1) abdominal cramps, 2) grossly bloody diarrhea, 3) absent or low-grade fever, and 4) stool specimens negative for the usual bacterial and parasitic enteric pathogens be reported to the Enteric Diseases Branch at (404) 329-3753. These reports and arrangements for examination of stool specimens should be made through the state epidemiologist and laboratory director as described previously (3).

References

1. Johnson WM, Lior H, Bezanson GS. Cytotoxic Escherichia coli O157:H7 associated with haemorrhagic colitis in Canada. Lancet 1983;1:76.

2. Riley LW, Remis RS, Helgerson SD, et al. Outbreaks of hemorrhagic colitis associated with a rare Escherichia coli serotype. N Engl J Med 1983;308:681-5.

3. CDC. Isolation of E. coli O157:H7 from sporadic cases of hemorrhagic colitis--United States. MMWR 1982;31:580, 585.

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