Strategies to Reduce Person-to-Person Transmission during WidespreadEscherichia coliO157:H7 Outbreak

Abstract

RESEARCHDuring the Escherichia coli O157:H7 outbreak in 2006 in the United States, the primary strategy to prevent illness was to advise consumers not to eat spinach. No widespread warnings were issued about preventing person-to-person (secondary) transmission. A disease transmission model, fi tted to the current data, was used to investigate likely reductions in illnesses that could result from interventions to prevent secondary transmission. The model indicates that exposure to contaminated spinach occurred early in the outbreak and that secondary transmission was similar to that in previous E. coli outbreaks (≈12%). The model also suggests that even a modestly effective strategy to interrupt secondary transmission (prevention of only 2%-3% of secondary illnesses) could result in a reduction of ≈5%-11% of symptomatic cases. This analysis supports the use of widespread public health messages during outbreaks of E. coli O157:H7 with specifi c advice on how to interrupt secondary transmission.W idespread distribution of contaminated spinach was implicated in an Escherichia coli O157:H7 (E. coli O157) outbreak in the United States in 2006. As of September 24, 2006, a total of 173 cases had been reported in 25 states; 88% of cases were reported over an 18-day period from August 19 through September 5, 2006 (1). The outbreak strain was particularly virulent, resulting in 1 death, 53% of patients being hospitalized, and a 16% rate of hemolytic uremic syndrome. At the time of our analysis, the potential extent of the outbreak was unknown because new cases were still being reported. The Centers for Disease Control and Prevention (CDC) and the US Food and Drug Administration advised consumers not to eat spinach as the primary strategy for protecting against foodborne transmission of E. coli O157 (2). No warnings, however, were issued regarding the prevention of person-to-person (secondary) transmission.According to recent studies on the extent of secondary transmission for E. coli O157 and other pathogens, the initially reported foodborne illnesses in the outbreak may have represented only a small fraction of a larger outbreak that included asymptomatic infections and secondary infections among household members of infected persons and other close contacts. Specifi cally, the E. coli O157 literature indicates that a large proportion (72%) of infections are asymptomatic (3), exposure to low doses can result in infection (4), and reported secondary transmission rates are on the order of 4%-16% (5). Further, outbreaks of shigellosis (6), cryptosporidiosis (7), and giardiasis (8,9) indicate that other highly infectious enteric pathogens can spread from person to person after being introduced into a community through water, food, or other sources (9). Recent adenovirus outbreak data indicate that persons with asymptomatic infection who are shedding virus can be a primary cause of continual transmission of infection (10). And in a prolonged giardiasis outbreak that occurred in late 2003 in a Boston, Massachusetts, suburb, 30 ...

Escherichia coliO157:H7: Animal Reservoir and Sources of Human Infection

“…Person-to-person transmission of EHEC may contribute to outbreaks from a primary source (Parry et al, 1998;Seto et al, 2007) and may reach 14% (Rangel et al, 2005) or higher; secondary cases occurred in 20=89 households with STEC O157 infection in the United Kingdom , and significant interpersonal spread was noted in 18-case O157 outbreak in Ireland, with identical=close PFGE patterns in isolates from patients and a rectal animal swab (Mannix et al,…”

Engineering and evaluation of a mouse/human chimeric antibody against Shiga toxin 2

“…serotype etiologically associated with HUS is generally believed to be O157:H7, such as what was observed in the STEC outbreak in the fall of 2006 in USA which was induced by contaminated spinach, and in the large-scale epidemic that happened in China in 1999-2000 (Seto et al, 2007). However, an unusual E. coli serotype O104:H4 was identified to be responsible for German STEC outbreak in 2011, which caused thousands of infection and HUS cases, demonstrating horizontal gene exchange event during enterobacteria natural evolution (Bezuidt et al, 2011).…”

Analysis of enteric disease outbreak metrics, British Columbia Centre for Disease Control, 2005–2014

“…Modelling may also permit assessment of combined intervention strategies, which more closely reflects real-world situations. Based on data from previous outbreaks, studies have used models to simulate the expected temporal distribution of cases (epidemic curve) and quantify the effect of interventions (3,4).…”

“…Outbreak data have also been used to assess the impact of interventions. Seto et al (2007) used data from a multistate outbreak of Escherichia coli O157:H7 in the United States to model control strategies and found that reducing secondary transmission by 1-25% could prevent 2-3% of secondary cases and 5-11% of infected and symptomatic individuals (3). Chen et al (2014) used data from a waterborne shigellosis outbreak at a school in China to examine the effect and optimal combination of five interventions on the attack rate and outbreak duration (4).…”