Measures of health status

Measures of health status:

1. Birth rate = number of births in a year X 1000 / mid-year population

2. Age/sex specific mortality rate = number of deaths in a year in specific age/sex group X 1000 / mid -year population of age or sex group respectively

3. Maternal mortality rate = number of maternal deaths in a given period of time X 100, 000 / total live births in the same period of time Maternal death is the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management but not from accidental or incidental causes.

4. Fertility rate = number of live births in a year X 1000 / mid-year population of women aged 15-44 years

5. Neonatal mortality rate = number of deaths of age < 28 days in a year / number of live births in a year

6. Perinatal mortality rate = number of stillbirths + deaths of age < 7 days, in a year X 1000 / total number of births (live births + stillbirths) in a year

7. Infant mortality rate = number of deaths of age < 1 year in a year X 1000 / number of live births in a year

8. Case fatality rate (%) = number of deaths in a year from a specific disease X 100 / number of cases of that disease in a year

9. Proportional mortality rate (%) = total number of deaths from a specific disease X 100 / total number of deaths from all causes

Life expectancy and health-adjusted life expectancy: They are general measures of population health status. Life expectancy is a statistical measure of the average time an individual is expected to live, based on the year of birth, current age, and other demographic factors including gender. Health-adjusted life expectancy (HALE) is the average number of years that a person is expected to live in good health by taking into account years lived in less than full health due to disease and/or injury. Life expectancy and HALE are based on specific population groups during a defined period of time. Individual life expectancies will vary substantially around this population average and the average will change over time.

Attack rate or incidence proportion/risk = number of new cases of disease during specified time interval /population at start of time interval

Secondary attack rate = number of new cases among contacts / total number of contacts

Consider an outbreak of shigellosis in which 18 persons in 18 different households all became ill. If the population of the community was 1,000, then the overall attack rate was 18 ⁄ 1,000 × 100% = 1.8%. One incubation period later, 17 persons in the same households as these “primary” cases developed shigellosis. If the 18 households included 86 persons, calculate the secondary attack rate.

Secondary attack rate = (17 ⁄ (86 − 18)) × 100% = (17 ⁄ 68) × 100% = 25.0%

Note that the denominator for secondary attack rate ((86-18) in the above example), excludes the cases that already had shigellosis hence were not at risk of re-acquiring the disease.

Herd immunity: It is the level of immunity to an infectious disease in the community that is able to prevent person-to-person spread of a disease. It is typically acquired through vaccination and/or prior illness leading to natural immunity. As a result of good herd immunity even unvaccinated individuals are less likely to get infected.