A revision of Shiga-toxin producing E. coli guidelines in Norway was helped by a survey and new scientific evidence.
In autumn 2016, Shiga-toxin producing E. coli (STEC) guidelines were modified accounting for evidence on the association between hemolytic uremic syndrome (HUS) and virulence profile of STEC strains.
The revised guidelines differentiate control measures and follow-up between cases with high-virulent and low-virulent STEC infection. Also, the number of stool samples for microbiological clearance is reduced from five to three for cases with high-virulent STEC and three to zero for people with low-virulent STEC. Previous guidelines did not accommodate for varying pathogenic potential of STEC.
The move is expected to decrease the number of STEC cases needing clearance, reducing socioeconomic impact on them and their families. It will also allow better use of time and resources on STEC surveillance and prevention by public health professionals.
Officials at Folkehelseinstituttet (Norwegian Institute of Public Health) are currently investigating an E. coli outbreak with five confirmed and two possible infections. Patients live in Hordaland, Aust-Agder, Trøndelag and Hedmark. One is a child, two are adults under 70 years old and four are over 70. Four people have developed HUS.
Notification of STEC infections is mandatory in most European countries but is voluntary in Belgium, France, Italy, and Luxembourg. It has been mandatory since 1995 to the Norwegian Surveillance System for Communicable Diseases at the Norwegian Institute of Public Health.
Strain on existing system
Between 1996 and 2016, 1,230 STEC infections were notified in Norway, of which 31 percent were hospitalized and 84 developed HUS. In 2013 to 2016, notified STEC cases increased from 193 to 239, largely due to introduction of culture-independent diagnostic tests and unselective screening of STEC.
This growth of less severe STEC challenged the existing system. Stringent precautions to prevent transmission such as 3 to 5 negative stool samples were onerous for patients and their families, especially when clearance was prolonged.
Impact was financial due to absence from work, either to avoid occupational risk for spreading the disease or to care for sick children with infection, and psychological for families where children were kept from kindergarten for an extended time.
In autumn 2016, researchers did a survey to describe control measures for STEC cases by different European public health agencies to inform the revision of measures and follow-up of cases in Norway. Findings were published in the Epidemiology and Infection journal.
Austria, Denmark, Finland, France, Greece, Ireland, Netherlands, Slovenia, Spain, Sweden, UK and Norway responded. Brussels and Flanders in Belgium followed the same guidelines but different than from Wallonia so were included separately in the analysis.
Eight respondents had updated their guidelines within the previous two years (2015 to 2016); the remaining six had updated them during 2007 to 2013. Ten refreshed guidelines following an outbreak or as routine procedure.
Discrepancies in recommendations of different countries existed for exclusions and microbiological clearance. Follow-up of cases and both asymptomatic and symptomatic close contacts, regarding exclusion periods and microbiological clearance, also varied.
In 2015, Denmark updated their guidelines due to new evidence of the association between HUS and different virulence profiles of STEC strains. Only Denmark differentiated control measures based on routinely Shiga toxin (stx) subtyping of all STEC isolates.
In all countries, but Norway, clearance was obtained with fewer than three negative stool specimens. Sweden treated symptomatic and asymptomatic contacts as cases and excluded them from work or school until they had microbial clearance.
Applying new rules to old infection data
Until autumn 2016, Norwegian recommendations were strict compared with other EU countries. For some cases, Norway requested five negative stool samples for microbiological clearance, almost double requirements in other countries.
Norway distinguishes control measures for high-virulent and low-virulent STEC to better target infection control and follow-up. Differentiation is based on the stx profile and clinical outcome. Only those with high-virulent STEC infections who belong to high-risk groups for secondary transmission of disease are followed-up.
People with high-virulent STEC infection are excluded until microbiological clearance, confirmed by three consecutive negative stool specimens taken 24 hours apart, with the first taken two to three days after recovery.
Those with low-virulent STEC infection can return to work or kindergarten 48 hours after recovery from diarrhea without microbiological testing.
Applying the new guidelines to 212 STEC cases, tested during 2016 where the stx profile was available, 44 percent would have been classed as infected with a low-virulent STEC. For the remaining 118 cases, only 73 had a known stx subtype. Of these, 53 percent would have been classified as carrying a low-virulent STEC.
This suggests that 63 percent of all 212 cases in 2016 would not have required follow-up under the revised guidelines. This proportion becomes 80 percent when counting only the 167 cases with sufficient virulence data. In contrast, following the previous guidelines, only 41 of 212 cases with a STEC infection did not require follow-up.
It is especially relevant as an increase in reported STEC cases is expected in Europe in the near future, mainly due to changes in diagnostic methods and screening procedures. Any rise will reinforce the need for revision of country-specific guidelines to allow better use of resources on control measures for STEC infections.
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