| Study participant | Definition |
|---|---|
| Index case | The first person in the household in whom laboratory-confirmed Bordetella pertussis infection is diagnosed by means of PCR. The index case may not be the first case in the household but is the first case that comes to the attention of public health authorities. |
| Primary case and coprimary case | The first member of the household to be infected with B. pertussis. This person may or may not be the index case. A coprimary case is a household member who becomes sick within 1 wk of symptom onset in the index case. Both case types must be epidemiologically linked and/or laboratory-confirmed. |
| Household contact | Any study-eligible person living in the household or regularly providing care in the home from 2 wk before onset of illness in the index case and who will still be living or providing care there within 8 wk of onset of illness in the index case. A child's caregiver is also considered a household contact. |
| Contact-cases | Household contacts who experience symptoms compatible with pertussis after the initial assessment and in whom pertussis is diagnosed by a positive PCR test result within 8 wk of disease onset in the index case. |
| Contact-controls | Household contacts who do not have a positive laboratory test result for pertussis during the entire study period (i.e., from 8 wk of disease onset in the index case) and remain asymptomatic during that period. |
| Asymptomatic PCR-positive contact | A PCR-positive household contact who does not manifest pertussis symptoms in the 2 wk before to 8 wk after onset of illness in the index case. Although it will be impossible to rule out whether these people are the primary case in the household, we will include them in the study and will account for this at the analysis stage. |
Note: PCR = polymerase chain reaction.