1. Disentangling / unmasking Alain Moren, Dublin, 2006 What is behind: The epidemic curve The rate

2. Behind the epidemic curve ?

3. Hepatitis A by date of onset Ogemaw county, Michigan, April - May 1968 281420262814202617 Days 0 5 10 15 Number of cases one case 30 days 15 days 50 days Exposure

6. Gastroenteritis by day of onset 12345678910111213 Days 0 10 20 30 40 50 Cases Common source ? Person to person ?

7. Number of cases One case Cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986 181920212223242526271716151314 Days 0 5 10

8. ProteinTotalCasesAR%RR suppl. YES 29 22763,3 NO 74 1723 Total103 3938 Cases of gastroenteritis among residents of a nursing home according to protein supplement consumption, Pa, 1986

9. Number of cases One case Early cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986 181920212223242526271716151314 0 5 10 Days

10. ProteinTotalEarly AR%RRCI 95% suppl.cases YES 29 14 486.93,2-15,8 NO 74 5 7 Total103 19 19 Early cases of gastroenteritis according to protein suppl. consumption Early cases = onset < 21 October

11. Number of cases One case Late cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986 181920212223242526271716151314 Days

12. ProteinTotalLate cases ARRRCI 95% suppl. % YES103302,50,7 - 8,9 NO 65812 Total751115 Late cases of gastroenteritis according to protein suppl. consumption, Pa, 1986 Late cases = onset > 20 October

13. ProteinTotalEarly cases ARRRCI 95% suppl. lab. + % YES 29 103511,74,2- 38,7 NO 74 2 3 Total103 1212 Early cases of gastroenteritis lab. confirmed according to protein suppl. consumption, Pa, 1986

14. Cases of gastroenteritis by date of onset, Latuque, Quebec, 1989 7-118-119-1110-1111-1112-1113-1114-1115-1116-1117-1118-1119-1120-11 0 10 20 30 40 50 60 70 Date of onset

15. Cases of gastroenteritis by date of onset, Latuque, Quebec, 1989 7-118-119-1110-1111-1112-1113-1114-1115-1116-1117-1118-1119-1120-11 0 10 20 30 40 50 60 70 Date of onset

17. Risk factors Restaurant Hotel Shop

19. Events Person - time denominator Behind the rate ? Sum of individual contribution Denominator

20. Vaccine efficacy Attack rate among vaccinated Attack rate among non vaccinated

21. Vaccinated Not vaccinated % with disease Epidemic duration VE based on attack rates (cumulative incidence) VE = ARNV - ARV ARNV

22. Assumptions Vaccine status as noted at begining of epidemic Vaccine status does not change during epidemic Epidemic duration is short Disease status as noted at the end of the epidemic If interested in VE by age group: ==> one individual stays in same age group during entire epidemic

23. 6 Incidence density rate among non vaccinated 6 Incidence density rate among vaccinated VE = IDRNV - IDRV IDRNV Rates expressed in person-time

24. VNV 6060 V V V V 2.53.5 6060 3030 0303 2.5 1 D M NV M Measles epidemic, duration = 6 months V 0606 NV

25. = 9 m 6 5 1 4 2 3 2 3 1 1 3 2 3 2 4 1 5 012345678012345678 Age (month) at beginning of epidemic Time spent in each Age group Epidemic duration = 6 months

26. Information needed ! Date of start and end of epidemic ! Date of birth ! Date of death ! Date of onset of measles ! Incubation period (median) ! Delay for protection from vaccine