A VEROCYTOTOXIN-PRODUCING E. COLI OUTBREAK WITH A SURPRISINGLY HIGH RISK OF HAEMOLYTIC URAEMIC SYNDROME, DENMARK, SEPTEMBER-OCTOBER 2012
In late September 2012, a paediatric department in a Central Copenhagen Hospital notified Statens Serum Institut (SSI) of four cases of haemolytic uraemic syndrome (HUS). This led to the initiation of an outbreak investigation.
HUS and infections with verocytotoxin-producing E. coli (VTEC) are individually notifiable in Denmark. Furthermore, VTEC infections are laboratory-notifiable. Around 180 cases are reported each year, of which serogroup O157 constitute 15–20% [1].
Previously, Denmark has experienced only two general outbreaks of VTEC infection. In 2006 an outbreak of VTEC O157 affected 25 cases, with organic pasteurised milk as the source [2]. In 2007, an outbreak of VTEC O26 affected 20 cases, with an organic fermented beef sausage as the source [3]. In addition, Denmark reported 26 cases during the large VTEC O104 outbreak in Germany in 2011 [4]. The annual number of HUS cases in Denmark ranges from two to six [1]. Subtyping of verocytotoxin genes are done at SSI as described in [5].
Outbreak investigation
For this outbreak, we defined a confirmed case as an individual with a laboratory-confirmed infection with VTEC O157 eae, vtx1a and vtx2a diagnosed after 1 August 2012, or a person diagnosed with HUS in the same time period and a serology-confirmed VTEC O157 infection. A probable case was a person without laboratory-confirmed VTEC infection, diagnosed with HUS after 1 August 2012, or a person diagnosed with VTEC O157 infection in the same period, but without subtyping, or a person diagnosed with VTEC eae, vtx1a and vtx2a infection in the same period, but without O-typing. The date 1 August was chosen in order to identify any early cases.
On 22 October, after laboratory confirmation of VTEC O157 in two patients, SSI notified Danish clinical laboratories of a possible VTEC outbreak to increase case ascertainment and reporting. We interviewed patients (or their parents for children under 15 years of age) by telephone, using a structured trawling questionnaire.
Early investigations had pointed to ground beef as the possible outbreak source, and information on purchase dates and other possible labelling information of ground beef was collected and presented to the supermarkets for further tracing of possible batch identification. The Danish Veterinary and Food Administration traced back the ground beef. SSI performed live-slide agglutination on the submitted isolates upon arrival, and all VTEC O157-positive isolates were typed immediately with the PCR protocol for subtyping of vtx genes [5]. Further testing included conventional (and confirmatory) O:H serotyping, Vero cell assay, fermentation of sorbitol, production of beta-glucuronidase, presence of additional virulence genes by dot blot hybridisation and/or PCR, and pulsed-field gel electrophoresis (PFGE). We asked patients who were culture-negative for VTEC O157 to submit a serum specimen for serology testing for antibodies against VTEC O157.
Findings
We identified 13 cases of VTEC O157 (11 confirmed and two probable). Eight cases had HUS. The cases belonged to nine families. Eleven reported symptoms, whereas two were diagnosed when we screened healthy family members. Date of disease onset ranged from 18 September to 28 October 2012 (Figure). The cases were distributed throughout the country, eight were female, and the median age was 14 years (range: 3–68 years).
Source: Eurosurveillance
Previously, Denmark has experienced only two general outbreaks of VTEC infection. In 2006 an outbreak of VTEC O157 affected 25 cases, with organic pasteurised milk as the source [2]. In 2007, an outbreak of VTEC O26 affected 20 cases, with an organic fermented beef sausage as the source [3]. In addition, Denmark reported 26 cases during the large VTEC O104 outbreak in Germany in 2011 [4]. The annual number of HUS cases in Denmark ranges from two to six [1]. Subtyping of verocytotoxin genes are done at SSI as described in [5].
Outbreak investigation
For this outbreak, we defined a confirmed case as an individual with a laboratory-confirmed infection with VTEC O157 eae, vtx1a and vtx2a diagnosed after 1 August 2012, or a person diagnosed with HUS in the same time period and a serology-confirmed VTEC O157 infection. A probable case was a person without laboratory-confirmed VTEC infection, diagnosed with HUS after 1 August 2012, or a person diagnosed with VTEC O157 infection in the same period, but without subtyping, or a person diagnosed with VTEC eae, vtx1a and vtx2a infection in the same period, but without O-typing. The date 1 August was chosen in order to identify any early cases.
On 22 October, after laboratory confirmation of VTEC O157 in two patients, SSI notified Danish clinical laboratories of a possible VTEC outbreak to increase case ascertainment and reporting. We interviewed patients (or their parents for children under 15 years of age) by telephone, using a structured trawling questionnaire.
Early investigations had pointed to ground beef as the possible outbreak source, and information on purchase dates and other possible labelling information of ground beef was collected and presented to the supermarkets for further tracing of possible batch identification. The Danish Veterinary and Food Administration traced back the ground beef. SSI performed live-slide agglutination on the submitted isolates upon arrival, and all VTEC O157-positive isolates were typed immediately with the PCR protocol for subtyping of vtx genes [5]. Further testing included conventional (and confirmatory) O:H serotyping, Vero cell assay, fermentation of sorbitol, production of beta-glucuronidase, presence of additional virulence genes by dot blot hybridisation and/or PCR, and pulsed-field gel electrophoresis (PFGE). We asked patients who were culture-negative for VTEC O157 to submit a serum specimen for serology testing for antibodies against VTEC O157.
Findings
We identified 13 cases of VTEC O157 (11 confirmed and two probable). Eight cases had HUS. The cases belonged to nine families. Eleven reported symptoms, whereas two were diagnosed when we screened healthy family members. Date of disease onset ranged from 18 September to 28 October 2012 (Figure). The cases were distributed throughout the country, eight were female, and the median age was 14 years (range: 3–68 years).
Source: Eurosurveillance
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