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Public Health Operational Guidance for Shiga toxin producing Escherichia coli (STEC) Case scenarios illustrating the use of STEC algorithm
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Prepared by: Peter Lamb SpT and Kevin Carroll CCDC
For feedback about these materials please email: [email protected]
© Crown copyright 2018
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Published August 2018
PHE publications PHE supports the UN
gateway number: 2018271 Sustainable Development Goals
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Scenario 1 Initial phone call from EHO Reporting a case of food poisoning reported to them by a Café worker. No diagnosis available. Case reported bloody diarrhoea. Initial response
Advise EHO to exclude case until 48hrs symptom free and results of diagnostic sample available
Advise EHO to enquire about other cases associated with the food business
Arrange for diagnostic stool sample through GP/PHE postal pot system if available
Local NHS lab results
Stx PCR POSTIVE
local culture O157 pending. Secondary response
Case still symptomatic
Continue to exclude
Complete STEC questionnaire (food handler, stx PCR positive and bloody diarrhoea). Regardless of local culture result the questionnaire will require completion.
Further data from local lab
local culture O157 NEGATIVE.
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Response
ACTIONS
Define as PROBABLE case
Complete STEC questionnaire if not already done
Give hygiene advice and warn further tests being done
Continue to exclude case until 48 hours symptom free
Case in risk group C – carry out risk assessment (Table 6 in guidance)
Identify contacts RISK ASSESSMENT
Case lives alone
Works as food handler
No other cases linked to his place of work
Case had returned from Morocco and became unwell several days after returning to UK.
Further Response
ACTION FOR CASE
Ask about evidence of transmission
Await GBRU in-house PCR result
NEXT STEPS
No evidence of transmission
Go to stage 2
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GBRU results
Initial case GBRU report: STEC O157 isolated (STEC PCR+, culture+) eae +ve, stx1 +ve and stx2 +ve
Case is now asymptomatic
Case has already had 2 consecutive samples taken at least 24 hours apart found to be stx PCR positive, local culture negative for STEC O157.
Response to GDW result
ACTIONS FOR CASE/CONTACT Define as CONFIRMED case
Re-inforce hygiene advice, STEC questionnaire already completed
No evidence of transmission
All actions as per STEC O157 management Have been completed
Case may return to work (although stx PCR positive local culture negative for O157 organisms not viable or present in very low numbers below level and represents a very low risk for transmission)
NEXT STEP No evidence of transmission. No further
public health action required
Discuss with microbiologist at reporting diagnostic lab to review why initial local culture result may have been negative for O157
Close incident
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Scenario 2 Initial data
2 year old child (Child A)
Stool sample submitted via GP
PCR - POSITIVE
Local culture - NEGATIVE
Comment 'persistent diarrhoea for 1 month'
No comment on bloody diarrhoea or foreign travel by GP/Lab Initial response
ACTIONS
Define as POSSIBLE case
Contact guardian by phone
Give hygiene advice
Exclude case until 48 hours symptom free
Ask about potential transmission NEXT STEP
Follow algorithm using information obtained from discussion with guardian
Discussion with parent/guardian
Child A has been symptomatic with on-and-off diarrhoea for two months
Symptoms: tummy ache, watery stool, 'sometimes with blood and mucous in stool.
Parent was concerned when they saw blood stool - and so took the child to their GP
Last episode of blood in stool a few days ago, although still experiencing intermittent diarrhoea
Child A attends nursery
Is currently toilet training and in nappies
Child A lives with Mother, Father, 8 year old sibling (Child B)
Father (Office Worker) and Child B have loose stools
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Secondary response
ACTIONS FOR CASE Change definition to PROBABLE case
Complete STEC questionnaire
Give hygiene advice and warn further tests being done
As the case is in risk group B start clearance, exclude until GBRU results or clearance achieved, whichever is sooner
Identify contacts and assess for symptoms (if not already completed)
ACTIONS FOR CONTACTS Arrange diagnostic sample for contacts
Give hygiene advice
Exclude contacts until 48 hours symptom free
NEXT STEP
Wait for GBRU in-house PCR result
Go to stage 2
Further information
Both symptomatic household contacts (father and child B) diagnostic samples are stx PCR - NEGATIVE
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GDW result
GDW result (child A) STEC - NOT isolated, eae +ve, stx1 -ve; stx2 -ve
STEC can lose stx genes during course of infection and culture. This may have happened.
Response to GDW result
ACTIONS FOR CASE AND CONTACTS Exclude until 48 hours symptom free
STEC infection not confirmed by GBRU
No further public health action required cease clearance
NEXT STEP
Close
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Scenario 3 Initial information
5 year old case Initially identified on GBRU report: STEC isolated (STEC PCR:+ culture:+) eae +ve, stx1 +ve and stx2 +ve
No other details Response to GDW result
ACTIONS Define as CONFIRMED case
Potential HUSEC
Complete questionnaire
Give hygiene advice
NEXT STEP
Complete risk assessment in response to the questionnaire
Questionnaire information
Case has history of recurring diarrhoea >1 month. No bloody stools
Case lives with 2 parents (both are food handlers) and one twin sibling. All asymptomatic.
Both children attend the same nursery
No other reports of GI symptoms by staff or attendees at the nursery Response
ACTIONS Exclude case
As case in risk group initiate clearance samples once symptom free
Exclude twin from nursery (as asymptomatic contact in risk group B (Refer to Table 7 in guidance)
Do not exclude parents reinforce hygiene advice
NEXT STEP
Wait for GBRU stx subtyping information
Go to Stage 3
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GBRU WGS result GBRU report that the WGS result is O unidentifiable (stx1c, stx2b) (Please note that initial GBRU testing (stage 2) detected eae. It is probable that there were other enteropathogenic E. coli (EPEC) in the culture enrichment broth that gave rise to the positive eae result.) SNP address 4.4.4.4.4.4.4
ACTION Follow up with GBRU, has strain
other virulence factors eg aggR or is it a serotype of concern?
GBRU have nothing of concern to report
ACTIONS No further PH action required
Case may return to nursery once 48 hours symptom free
Sibling may return immediately
If local policy is for local diagnostic lab to inform HPT of positive stx PCR results investigate why it appears not to have been reported by phone or via SGSS.
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Scenario 4 Initial data from BMS at local NHS laboratory
19 year old case
Stool sample submitted via GP
Stx PCR - POSITIVE
Local culture - PENDING
Comment “diarrhoea for a few days with traces of blood” Initial response
ACTIONS
Define as PROBABLE case
History of blood prompts HPT to follow up the case before local O157 culture result is available
Complete STEC questionnaire
Give hygiene advice and warn further tests being done
Exclude until 48 hours symptom free
Identify contacts NEXT STEP Follow algorithm and gather information on case and contacts
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You are called by local hospital gastroenterologist
Before questionnaire could be completed. The 19 year old presented as an emergency with a history of frankly bloody diarrhoea and abdominal pain.
CT scan revealed a pan colitis.
Case is hemodynamically stable but urine output has dropped off significantly and U&Es are deranged. Diagnosis is HUS. Case being transferred to tertiary centre for possible dialysis.
Local culture O157 – NEGATIVE Response to further information
***Revaluate risk assessment***
Manage as a CONFIRMED case Case has HUS therefore follow
STEC O157 management
Complete STEC enhanced surveillance
questionnaire ASAP.
Ensure diagnostic laboratory sends
samples to the GBRU as appropriate
(faecal and blood for serology)
Provide information and hygiene advice
Advise exclusion and clearance samples
for case according to risk group
Risk assess potential source(s) and
consider further control measures as
appropriate
Identify and risk assess contacts for
exclusion and/or microbiological clearance
Communication with relevant
organisations/ person(s) Including
Environmental Health Officers (EHOs),
GPs, child care settings and others
NEXT STEP
Wait for GBRU in-house PCR result
Follow up contacts as appropriate
Go to stage 2
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Information received
Case lives with Mother (works in a nursing home) Father (builder) and a 15 year old sibling.
Case has a partner, asymptomatic not in risk group
Sibling was symptomatic with diarrhoea for 2 days within the past week, but no longer symptomatic.
Secondary response
ACTIONS FOR CONTACTS Father - No public health action required
Mother (Risk group D) o Give hygiene advice o No exclusion or microbiological
clearance required (see Table 7 in guidance)
Sibling –Treat as PROBABLE case (case B) (see Table 7 of guidance) arrange for diagnostic sample. Case B is an epi link to case A.
Follow full STEC O157 management for case B (see left)
NEXT STEPS
Manage Case B as probable case (full details in section 2 of guidance), could be co-primary or secondary case
Information received
Case B Stx PCR – POSITIVE Local culture – NEGATIVE
Faecal specimen sent to GBRU
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GBRU results
Case A GBRU report: STEC isolated (STEC PCR:+ culture:+), eae +ve; stx2 +ve
Case B GBRU report STX genes detected (STEC PCR:+ culture:-) eae +ve; stx2 +ve
Response to GDW result
ACTIONS FOR CASE A (RED) Define as CONFIRMED case
Reinforce hygiene advice, STEC questionnaire already completed
There is evidence of possible transmission (Case B)
All actions as per STEC O157 management (should have been completed/in progress)
Review both case and contacts and route of transmission
ACTIONS FOR CASE B (Purple) Define as CONFIRMED case
Although confirmed by GBRU in-house PCR, STEC not isolated. Organism not viable or present in such low numbers that risk of transmission is likely to be very low.
No further public health actions for this case
NEXT STEP Case A wait for GBRU stx subtyping
information usually available about 16 days after initial laboratory report to HPT or 21 days after original sample taken
Go to stage 3
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GDW WGS subtyping information received
Case A: Sample result indicates the infection was caused by STEC O55:H7 (stx2a, eae)
Subtyping response
Action Check that all PH actions have been completed
Sibling likely to have been infected with the same strain
From the history you decide it is likely that this is a co-primary rather than secondary transmission event
Source of infection for both cases is probably a livery stables
Close
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Scenario 5 Initial information
Initial adult case identified on GBRU report isolated (STEC PCR+, culture+) eae +ve, stx1 +ve and stx2 +ve
Response to GDW result
ACTIONS Define as CONFIRMED case
Complete questionnaire
Give hygiene advice
NEXT STEP
Risk assessment in response to questionnaire noting that it is now about 11 days since the original sample was collected
Questionnaire information
Case is now asymptomatic >48hrs
Case lives with 3 adults not in risk groups. All asymptomatic.
Works in a bar/restaurant
No other reports of GI symptoms by staff or customers at the bar/restaurant Response
ACTIONS There is no evidence of transmission
Normally no further public health actions are required. However if there are concerns it is reasonable to carry out risk assessment to determine need for exclusion until final WGS information is available.
Investigate why case not notified
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GBRU WGS Subtyping information received
Sample result indicates the infection was caused by STEC O91:H14 (stx1a,stx2b, eae)
Subtyping response
Action Not a HUSEC strain
No further public health action required. He can return to work if excluded while waiting for this result
Close
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Scenario 6 Initial data
Adult
Stool sample submitted via GP
PCR - POSITIVE
Local culture - NEGATIVE
Comment '5 day history of diarrhoea'
No comment on bloody diarrhoea or foreign travel by GP/Lab Initial response
ACTIONS
Define as POSSIBLE case
Send warn and inform leaflet to patient with copy to GP
NEXT STEP
No further action required until any GBRU result becomes available
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Further information received
GP has received copy of the letter and formally notifies HPT of the case and also reports that patient did have bloody diarrhoea and might be a food handler. It is now 6 days after the sample was collected.
ACTIONS
Re-define as PROBABLE case
Complete questionnaire with patient and risk assess.
RISK ASSESSMENT
Case confirmed to be food handler [Group C]
No evidence of transmission to staff or patrons
Case has been asymptomatic for >48hrs.
NEXT STEP
Review risk assessment to determine whether restriction/redeployment may be appropriate whilst awaiting results of microbiological testing
If not appropriate, exclude case until microbiological clearance completed
Wait for GBRU results
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GDW result
STEC isolated (STEC PCR:+ culture:+) eae +ve, stx1 +ve and stx2 -ve
ACTIONS
Change definition to CONFIRMED case
No further public health action required because there is no evidence of transmission and case has been symptom free for > 48 hrs.
If clearance regime has been started this can be stopped.
NEXT STEP
Wait for GBRU WGS result to upload to case record
Case can return to work
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GBRU WGS subtyping results GBRU report that the WGS result is STEC O26:H11 (stx1a, eae)
ACTIONS FOR CASE
No further public health action required cease clearance
NEXT STEP
Close
