Field Epidemiology in Practice: Investigating an Acinetobacter Outbreak

1. Field Epidemiology in Practice: A Hospital Outbreak of Acinetobacter Suzanne Beavers, M.D EIS Officer Kentucky Department for Public Health

2. Environment Agent Host Infectious Disease Epidemiology Distribution and determinants of disease frequency . . . . . . application to public health problems.

3. Why initiate an investigation? • Characterize the problem • Control and prevention • Research-answer scientific questions • Training of epidemiologists • Political/legal requirement

4. 10 Steps of a Field Investigation • Prepare for field work • Establish existence of outbreak • Verify diagnosis • Define and identify cases • Orient data in terms of time, place, person • Develop hypotheses • Evaluate hypotheses • Plan additional studies • Implement control and prevention measures • Communicate findings Adapted from Field Epidemiology ed. Gregg MB

5. Field Investigations in Healthcare Facilities • Infections common, epidemics uncommon • Patients highly susceptible to infection • Colonization common, transmission not always found • Significant financial implications

6. Field Investigations in Healthcare Facilities • Epidemiology determines questions to ask • Laboratory provides answers • EPI and LAB together “solve” most outbreaks (especially true for outbreaks in healthcare facilities) Epidemiology + Microbiology = Outbreak Success

7. Field Investigations in Healthcare Facilities • Surveillance • cultures • Environmental • samples • Culture ID • Susceptibility • testing • Isolate typing Surveillance • Provides first evidence of outbreak • Often detected by microbiology • Line list of cases • Epi-curves • Case-Control study • Exposure risks Epidemiologic Studies Confirmatory Studies • Patient isolation • Enhanced disinfection • Suspend procedure or • close unit Local Interventions Adapted from Ostrowsky and Jarvis Efficient Management of Outbreak Investigations

8. Acinetobacter Outbreak Investigation

9. Acinetobacter spp. Background • Gram-negative bacillus • Prior healthcare- associated outbreaks • Traditionally associated with ICUs • Increasing cause of serious illness Image courtesy of Acinetobacter.com

10. Microbiology • Ubiquitous: • Widely distributed in nature (soil, water, food, sewage) & the hospital environment • Survive on moist & dry surfaces • 32 species • >2/3 of Acinetobacter infections are due to A. baumannii • Highly antibiotic resistant

11. Major infections due to Acinetobacter • Ventilator-associated pneumonia • Urinary tract • Bloodstream infection • Skin/wound infections • Endocarditis • Peritonitis

12. Acinetobacter Ventilator-Associated Pneumonia • Acinetobacter accounts for 5-25% of all cases of VAP • Risk factors: • Advanced age • Surgery • Use of antimicrobial agents • Invasive devices • Prolonged ICU stay

13. Acinetobacter spp. Outbreaks • About 80 outbreaks in published literature over past 30 years • Outbreaks divided between respiratory, non-respiratory sites • Respiratory sites commonly related to ventilators • Variety of other sources recognized, including cell phones, mattresses, Bear huggers, common source medications *Ryan MP, et al, 2006 **Coenye T, et al, 2002 and Vaneechoutte M, et al, 2001

14. Acinetobacter Outbreak InvestigationVerify existence of outbreak • DPH notified in October, 2006 • Hospital A in KY has increased number of cases • 75 patients with culture-positive Acinetobacter since January, 2006

15. Verify Diagnosis • Goal is to rule out: misdiagnosis laboratory error • Examine case-patients • Review medical records • Confirm laboratory testing

16. Identify and Count Cases • Goals: • Identify maximum number of cases • Exclude noncases • Consider spectrum of manifestation (colonized vs infected) • Develop Case Definition • Set of conditions • Specific time period • Specific location

17. Identify and count cases • Conduct systematic search • Use multiple sources • Construct a line list

18. Orient Data • Person • Place • Time

19. Time-Ordering Key Events • Onset of illness in cases and contacts • Period of exposure to causal agents or risk factors • When treatments began • When control measures implemented • Potentially related events or unusual circumstances

20. Time • Epidemic curve: # of cases by time of onset • Configuration permits inferences • Agent known: use incubation period to look back at exposure • Agent unknown, but common event likely: postulate agent by determining the incubation period • Construct relative to specific sites or groups

21. Acinetobacter outbreak

22. Place • In a general outbreak: • Place of residence • Place of occupation • In a healthcare setting: • Floor or unit • Operating room

23. Person • Thoroughly describe the case group • Identify factors shared in common by cases • Obtain denominators to derive rates • Compare groups

24. Formulate and test hypothesis • Goal: explain the problem • Use comparison group(s) • Case-control study • Cohort study • Consider causation

25. Compare Hypothesis with established facts • Environmental/staff cultures may be needed • Performed to aid in the investigation once theories are generated • Less valuable in generating hypotheses

26. Plan More Systematic Study • Control measures • Continued data analysis

27. Implement Control Measures • Eliminate/treat source • Prevent further exposures • Active surveillance • Protect at-risk population • Enforce isolation precautions • Cohorting • Close/clean contaminated areas of hospital

28. Thank you!