Medical charts of all persons who were hospitalized and reported with confirmed cases of E. coli O157:H7 to the New York State Department of Health's Communicable Disease Surveillance System (CDSS) in 1998 and 1999 were reviewed according to a standardized survey form. A HUS case was defined as occurring in a patient with acute diarrhea who was hospitalized with E. coli O157:H7 infection and in whom confirmed or probable postdiarrheal HUS developed. A confirmed HUS case was defined as occurring in a patient with a clear history of acute diarrhea who showed the following signs: hemolytic anemia with microangiopathic changes, renal insufficiency (creatinine level >1.0 mg/dL in a child <13 years of age or >1.5 mg/dL in an adult, or >50% increase over baseline), and thrombocytopenia (platelet count <150,000/μL). A probable HUS case was defined as occurring in a patient with acute diarrhea with all the above signs except microangiopathic changes in the blood smear. Controls were hospitalized patients with E. coli O157:H7 infection without HUS. Demographic, clinical, and laboratory characteristics were abstracted from medical charts. Statistical analysis was performed by using SAS software (SAS Institute, Cary, NC, USA). A multiple logistic regression analysis was performed to identify factors associated with development of HUS.
In 1998 and 1999, the CDSS received reports of 1,170 cases of E. coli O157: H7 infection. Of these, 255 patients (21%) were hospitalized and 238 (93%) had medical charts available for review. Thirty-six (15%) patients were confirmed (n = 29) or probable (n = 7) HUS case-patients, and 202 E. coli O157:H7–infected patients without HUS were identified as controls. The risk of HUS was highest among children <5 years of age, compared with patients >65 years (odds ratio [OR] 4.9, 95% confidence interval [CI] 2.2–11.8). Sixty-nine percent of HUS patients were female compared with 61% of controls (OR 1.5, 95% CI 0.8–3.4). The hospital stay was significantly longer for HUS patients than controls (median hospital stay 13 vs. 3 days). Five HUS patients (14%) died, including 2 children <5 years of age, compared with 2 controls (1%).
Forty percent of all patients had vomiting, and 85% had bloody stool. These factors were not significantly different between patients and controls. Eleven (31%) case-patients and 78 (38%) controls were treated with antimicrobial drugs (not significant). Antimicrobial treatment was reported in 11 patients before the diagnosis of HUS: 6 received antimicrobial drugs primarily for other conditions (e.g., urinary tract infection, otitis media, venous line sepsis), 1 had treatment stopped once E. coli O157:H7 was diagnosed, and we could not tell whether drug regimens were completed or discontinued in 4 patients. HUS patients were more likely than non-HUS controls to have fever (OR 3.2, 95% CI 1.6–6.5). The duration of diarrhea before hospitalization was significantly longer for HUS patients than for non-HUS controls (median 4 vs. 2 days).
Proteinuria and hematuria were observed significantly more often among the case-patients. Twenty-three (64%) patients had proteinuria at admission, whereas 37 (18%) controls were admitted with proteinuria (OR 7.8, 95% CI 3.6–17). Hematuria at admission was reported in 23 (64%) patients and 57 (28%) controls (OR 4.5, 95% CI 2.1–9.4). Twenty-nine (81%) HUS patients vs. 90 (44%) controls had leukocyte counts >13,000/μL (OR 5.2, 95% CI 2.2–12.3) at admission (). Factors associated with HUS in univariate analysis (age <5 years, outbreak case, fever, hematuria, proteinuria, leukocytosis at admission, and duration of diarrhea before hospitalization >3 days) were included in the multivariate analysis. The following variables were associated with HUS development in the multivariate analysis: proteinuria (OR 6.7, 95% CI 1.9–24.1), duration of diarrhea before hospitalization >3 days (OR 6.2, 95% CI 2.2–17.4), age <5 years (OR 5.9, 95% CI 1.9–17.6), and leukocyte count >13,000/μL (OR 4.4, 95% CI 1.6–12.6). Factors such as outbreak involvement, hematuria and fever were not associated with HUS development ().
Characteristics of hospitalized Escherichia coli O157:H7 patients by HUS case status, New York, 1998–1999*
Multiple logistic regression analysis of risk factors associated with HUS, New York, 1998–1999*