Because cleaning and hygiene practices within the home would probably affect the dependent variable, infectious disease symptoms, we collected extensive data on cleaning and hygiene practices at baseline and at quarterly intervals. The Home Hygiene Assessment Form is a 31-page interview booklet that includes questions about demographic characteristics and illness (age, sex, ethnicity, country of birth, hours per week spent outside the home, type of work for adults, school or child-care arrangements for children, state of health, and presence of chronic diseases), home hygiene practices (54 items), and other relevant household factors (numbers and ages of household members, size of living space, presence of pets and visitors, type of building, and heating and cooling systems). We also asked participants about their attitudes and beliefs about how “germs” are spread and what they did to prevent infections in their home. The components of the instrument were originally derived from a literature search, focus groups of consumers, and a panel of environmental sanitation experts. The Home Hygiene Assessment Form was tested extensively for validity and reliability (16). Whenever possible, direct observations were made to confirm self-reports.