Infectious Disease Epidemiology, Module 3 Surveillance & Outbreaks

ANN JOLLY 2 Definition n “Ongoing systematic collection, analysis, and interpretation of health data essential to the planning, implementation, and evaluation of public health practice, as well as the timely dissemination to those who need to know” Centers for Disease Control. Comprehensive plan for epidemiologic surveillance. 1986

ANN JOLLY 3 Surveillance objectives n Monitor geographic and temporal trends n Monitor occurrence u With or without intervention u Planning u Further study n Investigate abnormal events n Prevent

ANN JOLLY 4 Public Health Law - Communicable Disease Control n Reporting and surveillance n Investigation as to source n Examination n Treatment n Isolation/quarantine u with or without judge’s permission u order with or without a warning of an order

ANN JOLLY 5 Reporting n Legislation requires the report u name, address, locating and demographics u laboratory data u clinical u treatment u source, contact data n Reportable by; u Laboratory u Health professionals

ANN JOLLY 6 Case definition n Defined by government u As part of regulations or Act u includes disease of unusually high numbers u Or disease with unusual manifestations ( high fatality) n Laboratory test component n Clinical n Or both n Ad hoc u Take an inclusive list of 80-90% of first 3-5 presenting cases at least u Be aware that agent may change, and hosts may become immune.

ANN JOLLY 7 Surveillance & Management n Ensure the case, and contacts are properly managed n Monitor the number of cases for unusual changes u risk, manifestation, affected population, geographic area n Consists of : u collection u compilation u analysis u dissemination

ANN JOLLY 8 Surveillance tasks 1. Set objectives n Monitor 2. Collect data n Notifiable disease reports 3. Analyse data n Preliminary associations by person or place 4. Disseminate n To public health colleagues 5. Hypothesis formation n To determine source eg, contaminated water

OUTBREAKS!!

ANN JOLLY 10 Outbreak steps 1.Confirm existing cases 2.Verify that outbreak exists 3.Describe outbreak in terms of; u Person u Place u Time 4.Hypothesize source, agent 5.Identify populations at risk 6.Test hypothesis (case control study) 7.Disseminate analysis, and prevent

ANN JOLLY 11 Outbreak tasks Repeat as often as necessary n Compile information n Draw conclusions from info (several) n Form hypothesis and collect the relevant information n Test hypothesis n Reformulate hypotheses

ANN JOLLY 12 Confirm diagnosis n False positive n Normal flora? u N. meningitidis u Streptococcus pyogenes n Carrier state n Contamination during collection n Lab. Error n Multiple infections n Data entry error

ANN JOLLY 13 If no diagnosis n Some indication of organism u System affected; enteric, respiratory n Incubation period n Frequency distribution of signs, symptoms

ANN JOLLY 14 Normal incidence? n H 0 All months which can be reasonably compared with this one have similar numbers of cases n H 1 All months are not similar, and some have significantly higher numbers of cases ( p<0.05)

ANN JOLLY 15 How many cases are normal? Frequency distribution, monthly numbers of infectious syphilis cases, British Columbia,

ANN JOLLY 16 Chart cases over time Infectious syphilis, British Columbia Sept 1995 – 1997

ANN JOLLY 17 Chart cases over time Infectious syphilis, British Columbia, Sept 1995 – 1997

ANN JOLLY 18 Advantages of threshold n Defines clearly when outbreak starts u Helpful in justifying more funding u Compare cases before and after start to detect possible differences n Defines when outbreak is over u Keep threshold constant during outbreak u Compute thresholds for seasonal infections n Note; allow for 5% error in detecting an outbreak will be indicated incorrectly

ANN JOLLY 19 Describing the epidemic n Time u Period of outbreak u Use diagnosis to estimate exposure n Place u Geographic distribution of cases F Common venues among cases F Spot maps n Person u Attack rates by age u Gender u Race

ANN JOLLY 20 Identifying etiologic agent n Pathogen will narrow the range of exposure n Hypothesize (may be more than one) u The people exposed to “x” will have a higher attack rate than those not exposed, p<0.05 u Χ 2 tables for food

ANN JOLLY 21 Implementing control measures n Immunization u passive, active n Destroy contaminated food n Boil, chorinate, filter water n Inspect n Remedy n Close n Isolate, quarantine

ANN JOLLY 22 Evaluate intervention n Monitor cases n Report investigation u Introduction u Background u Methods of studies conducted u Analysis and Results u Control measures u Recommendations

ANN JOLLY 23 Investigation of a foodborne illness, Winnipeg, 1991 n Bride became ill with diarrhoea u Admitted to hospital June 9 u Other reports of food borne illness too n Wedding June 1, 155 guests n Public health inspector investigated chain of events u Obtain info on guests u Menu u Food preparation and transport u Identify food handling practices which may contribute

ANN JOLLY 24 Investigation, cont. n Medical Health Officer u Requested guests to complete a questionnaire F Age, gender, address F Symptoms, laboratory tests, time off work F Food eaten June 1 and 2 n Samples, bride + 8 others n Leftover food tested u Salmonella, B. cereus, Campylobacter

ANN JOLLY 25 Results, chain of events n Roast turkey n Dressing n Mashed potatoes n Corn n Cabbage rolls n Meatballs n Coleslaw plain& creamy n Mushroom gravy n Rolls n Cranberry sauce n Black forest cake n Tea, coffee, milk n Baker Boy catering cooked in Selkirk n Transported to venue 05:30 pm n Served 6:30 pm?? Turkey served later n Meal over at 8:30 n Leftovers in containers for family n Only coleslaw refrigerated due to space n Late night meal 22h00 n Leftovers served next day

ANN JOLLY 26 Onset Histogram, Winnipeg, 1991, food borne illness

ANN JOLLY 27 Age specific attack rate

ANN JOLLY 28 Gender ILL (%)WELLTOTAL FEMALES12 (19.4) 5062 MALE15 (32.6) 3146 TOTAL27 (25.0) 81108

ANN JOLLY 29 Symptoms Cases, n=31Percent Diarrhoea Weakness Abdominal pain Anorexia Nausea Fever Headache Vomiting618.8

ANN JOLLY 30 Χ 2 tables for menu items Coleslaw dressed ILL (%)WELLTOTAL Yes13 (13.2) 2841 No14 (14.3) 4155 TOTAL27 (28.0) 6998

ANN JOLLY 31 Laboratory results n Salmonella hadar in individuals n Leftover corn Salmonella hadar u Avian type n Maximum 72 hour incubation period n Why did the corn test positive? n One of the 5 people who were ill before the wedding was +ve for S. hadar

ANN JOLLY 32 Control measures n Restricting preparation of turkey to one area n Only certain staff to prepare meat n All raw meat processed at one time n Restricting sets of implements to only meat processing n Correct food storage

ANN JOLLY 33 Summary n Verify the diagnosis n Compare numbers of cases with normal n Describe the outbreak by; u Person u Place u Time n Develop hypotheses of etiologic agent, test n Control n Evaluate

ANN JOLLY 34 References n Teutsch, SM and Churchill, RE, eds. Principles and practice of public health surveillance. Oxford University Press, 1994 n Morbidity and Mortality Weekly Report. Supplement, December Proceedings of the 1992 International Symposium on Public health surveillance. Vol 41. n Thacker SB, Berkelman RL. Public health surveillance in the United States. Epidemiologic Reviews 1988;120: