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BACKGROUND: Los Angeles County (LAC) has had an increase in Shiga toxin-producing Escherichia coli(STEC) reports in recent years, primarily due to an increase in non-O157 serotypes. As a result the workload of the Public Health staff has expanded. LAC compared illness severity, duration, and communicability between O157 STEC and non-O157 STEC cases to determine if non-O157 cases should be managed differently.
METHODS: Illness severity, duration, and communicability by O157 status was assessed using all STEC cases reported in LAC from 2006-2011. Communicability by O157 status was assessed by comparing the following indicators 1) number of households with multiple STEC cases in the same household 2) average duration of shedding for Sensitive occupation/situation(SOS) cases 3) number of SOS cases remaining positive on the first clearance specimen 4) number of specimens collected before clearance of infection.
RESULTS: From 2006-2011 LAC had a total of 270 STEC cases reported, 179 non-O157 and 91 O157). As compared to O157 cases, non-O157 cases had less frequent bloody diarrhea (34% for non-O157 vs. 81% for O157, p<0.01) and were hospitalized less often (9% for non-O157 vs. 34% for O157, p<0.01), but had a comparable illness duration (9.2 days for non-O157 vs. 10.5 days for O157, p=0.23). The number of instances where multiple confirmed STEC cases were identified within the same household (4%) was also similar by O157 status (4% for non-O157 vs. 5% for O157, p=0.2). The percent of all SOS STEC cases (N=43) remaining positive on the first clearance specimen (60%) was similar by O157 status (61% for non-O157 vs. 60% for O157, p=0.3). The average clearance time for an SOS case (31.6 days) was also similar by O157 status (35.0 days for non-O157 vs. 25.5 days for O157, p=0.15). The average number of clearance specimens obtained prior to a negative result (3.2 specimens) was slightly higher among the non-O157 serotypes (3.8 specimens for non-O157 vs. 2.5 specimens for non-O157, p=0.05). The non-O157 serotypes reported in LAC over this time period (N=91) include O103:H2 (18%), O111:NM (18%), O26:H11 (16%) and other/undetermined (48%).
CONCLUSIONS: The results of this study suggest that non-O157 STEC infections are more common in LAC and less severe than O157 infections, but would appear to be just as communicable. Public health control measures, including clearance of SOS cases, should be performed regardless of STEC serotype, to prevent additional illnesses. Further studies to determine convalescent shedding period of STEC would help guide disease control recommendations for SOS.