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

Behind the epidemic curve ?

Hepatitis A by date of onset Ogemaw county, Michigan, April - May Days Number of cases one case 30 days 15 days 50 days Exposure

Gastroenteritis by day of onset Days Cases Common source ? Person to person ?

Number of cases One case Cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October Days

ProteinTotalCasesAR%RR suppl. YES ,3 NO Total Cases of gastroenteritis among residents of a nursing home according to protein supplement consumption, Pa, 1986

Number of cases One case Early cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October Days

ProteinTotalEarly AR%RRCI 95% suppl.cases YES ,2-15,8 NO Total Early cases of gastroenteritis according to protein suppl. consumption Early cases = onset < 21 October

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

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

ProteinTotalEarly cases ARRRCI 95% suppl. lab. + % YES ,74,2- 38,7 NO Total Early cases of gastroenteritis lab. confirmed according to protein suppl. consumption, Pa, 1986

Cases of gastroenteritis by date of onset, Latuque, Quebec, Date of onset

Cases of gastroenteritis by date of onset, Latuque, Quebec, Date of onset

Risk factors Restaurant Hotel Shop

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

Vaccine efficacy Attack rate among vaccinated Attack rate among non vaccinated

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

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

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

VNV 6060 V V V V D M NV M Measles epidemic, duration = 6 months V 0606 NV

= 9 m Age (month) at beginning of epidemic Time spent in each Age group Epidemic duration = 6 months

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