Appendix A – Calculations of ARF recurrences per 100 patient-years

Acute rheumatic fever (ARF) recurrence rate per 100 patient-years is the number of ARF recurrent events per 100 patient-years during the period that a person is prescribed prophylaxis and, therefore, at risk of ARF recurrence. The time prescribed prophylaxis is used to determine time at risk of ARF recurrence because a person is prescribed prophylaxis if they have been previously diagnosed with ARF and/or rheumatic heart disease (RHD) and could therefore have an ARF recurrence. The numerator is the number of recurrences. The denominator of the rate is calculated by adding the time prescribed prophylaxis of all patients, where each patient’s exposure time is defined as days spent in a pre-determined time period (that is, a year), ended only by events such as death or the end of the prescription period. The rate is then divided by the total number of days per year to get the value for each patient-year and then multiplied by 100.