Techniques and limitations of the field epidemiology, investigation and control of VTEC outbreaks

1. Techniques and limitations of the field epidemiology, investigation and control of VTEC outbreaks Margot McLean - Medical Officer of Health Regional Public Health Dianne Morrison - Health Protection Officer Community and Public Health

2. Public health units • Who we are • Wider role of PHUs includes health promotion and school nursing • Regulatory health protection functions • Role in notification, surveillance and outbreak control

3. Notification of Cases and Outbreaks • Notifications received from: • Direct laboratory • GPs • Hospital based practitioners • Notification from the public due to an increase in GI illness in a community, group, etc • Data entry of cases into Episurv and regular review

4. Single case of VTEC – Initial Response • When did the person become sick? • How sick are they? • Follow up according to national and local protocols

5. Timeline from illness to notification • Infection • 2-10 day inc period (median 3-4 days) • Onset • 1+ days before see Dr • Dr visit • Drs often don’t request specimens unless diarrhoea for >3days, or blood present in stool • Notification can be made on suspicion • Specimen collection • Case collects specimen and returns to GP or to lab • Specimen analysis • May not be tested for VTEC; unless child under 5, blood in stools (national variation) • Specimen processed and cultured; 48+ hours • Results • Communicated to Dr and patient • Notification • Direct lab notification and via Dr (GP or hospital based) • Contact case • Contact details (need to be sought if lab notification) • Case may be in hospital (visited), may not respond to phone calls, etc.

6. Case Interviews • Interviewed by in person or by phone • ESR Case Report Form (CRF) and/or specific questionnaire • Patient recall affected by: • Time between illness and notification • Age of case: especially if old or young • Severity of illness • Diary or event to relate activities to • Who administers questionnaire? • HPO (EHO in some juristictions) • Experience of interviewer and knowledge of VTEC • Additional complications/delays if case transferred to Starship Hospital (if requires dialysis, etc)

7. Case Finding • Who else may be affected? • Exposure to same source / environment (co-primary cases) • Person-to-person transmission (secondary cases) • Asymptomatic cases: • Assess type/nature of exposure • Seek medical attention if symptoms develop • Clearance specimens if: • At high risk of transmitting it to others

8. Case Management • If not in a high risk occupation or situation: • case advised to stay away until asymptomatic for at least 48 hours • High risk cases excluded from work, and pre-school until: • 2 consecutive negative faecal samples taken at least 48 hours apart • Symptomatic contacts: • managed as cases until lab results known, including exclusions from high risk occupations and situations • Advice given: • nature of infection, mode of transmission, prevention of spread, hand hygiene

9. Sampling • Sample collection on case-by-case basis: • Food, water, environmental • Laboratory availability: • Location, weekend/holiday availability • Transport of samples to laboratory: • Remoteness from laboratory • Transport options / timeframes • Results and serotyping: • 48 hrs and longer for serotyping results

10. Site visits • To visit or not? – hard to determine source for single case • Farms have known risk factors – generally give advice only, depends on situation • Food or food premise strongly implicated • Environmental setting – dependent on scenario

11. Risk Assessment • Assess setting, likely sources, exposed population • Refer to surveillance information • Undertake interventions and control measures as appropriate • Whose jurisdiction are these? • Health, NZFSA, MAF, DoL, etc

12. Response to 2 or more VTEC notifications • Or- when is it an outbreak? • Look at number of cases vs expected… any obvious links between cases • Establish working case definition • Case finding – labs, hospital, GPs • Look on Episurv and EARS alerts • Check with ESR – laboratory and epidemiology staff

13. Types of outbreaks • Person-to-person • Point source (e.g. petting farm) • Common source, with local distribution or national distribution (including food from overseas)

14. Outbreak Team • Role of outbreak team: • Investigate – epidemiology and environmental • Control of outbreak • Communicate to stakeholders • Quality improvement – Review, report and follow-up on recommendations

15. Outbreak Response • Is a CIMS approach required? • Who needs to be involved? • Assign roles and responsibilities • Match response to situation • Redeploy staff

16. Coordinated Incident Management System (CIMS)

17. Communications and the Media • Stakeholders include: internal, health sector, public • Decide on media strategy • Assign communications role and key messages early • Multi-agency or many health districts – adds to complexity

18. Outbreak Investigation • Establish working case definitions (confirmed and probable) • Determine type of investigation; cohort vs case-control study – national outbreak requires national leadership • Case finding – labs, primary care, public • Questionnaire design • Determine interviewing methods and train staff

19. Outbreak Investigation • Analyse data collected • Investigate suspected sources • Control and prevention: • Should start as early as possible • Tension between acting early and having solid evidence • Aim is to stop transmission • Debrief, write outbreak report and implement recommendations

20. Recent national VTEC outbreak • 14 cases with indistinguishable or closely related PFGE pattern • Involved several PHUs in North Island • National case control study was done • Inconclusive results

21. Reflections from a public health unit perspective Challenges: • PHUs have slightly different approaches and questionnaires • Difficulty of going back to cases with new questionnaires, time-delay and boredom with our questions! • Workforce issues – time and expertise for interviewing • Control selection is critical – need good epidemiology advice • Co-ordination of tracebacks • Lead agency role not always clear in national outbreaks

22. Recommendations • Standardise VTEC follow up – needs inclusion in CD Manual • Standardise questionnaires used across country • Public health staff training and upskilling • Use of trained interviewers for major outbreaks e.g. use of telephone interviewing service • Development of a ‘control bank’ • Clarify central agency roles in national outbreaks of foodborne illness - lead agency, media spokesperson, feedback to stakeholders.