Measures of Disease Frequency

Abstract

1. Measures of disease frequency: a. Clarify the significance of a particular health problem b. Help guide resource allocation c. Provide basic insight into the pathogenesis of disease 2. Point prevalence describes the amount of disease at a particular point in time. 3. Incidence describes the number of new cases of disease that develop over time. 4. Incidence may be expressed as incidence proportion or incidence rate. 5. Incidence rate accounts for follow-up time 6. Measures of disease frequency can be stratified, or broken up, by person, place, or time characteristics to gain insight into a disease process. In December 1998, a 55-year-old woman presented to her local emergency department complaining of profound weakness and difficulty walking. She first noticed pain and weakness in her shoulders about 7 days earlier. The weakness progressed to involve her thigh muscles; she then developed nausea and noticed that her urine appeared dark. Over the next 48 h, her weakness further intensified and she became unable to stand on her own power. Her previous medical conditions included high blood pressure, asthma, and high serum cholesterol levels. Her father had died at an early age from heart disease. She did not smoke cigarettes and rarely drank alcohol. Her regular medications included aspirin, diltiazem, and cerivastatin. She first started taking cerivastatin 2 weeks earlier to treat high cholesterol levels. She appeared ill. There was no fever, the blood pressure was 140/95 mmHg, and the pulse was 48 beats/min. She was unable to raise her hips or her shoulders against gravity and her quadriceps muscles were diffusely tender. The rest of her physical examination, including neurological function, was normal. The urine was dark amber in color. Laboratory testing revealed a serum creati-nine level of 8.9 mg/dl, indicating severe kidney failure, and a serum potassium level of 7.6 mEq/liter (normal level is 2.5–4.5 mEq/liter). She was admitted to the hospital for emergent dialysis.