1. LANCET 1: 1376 (1984).
2. MORBIDITY AND MORTALITY WEEKLY REPORT 30: 250 (1981).
3. MORBIDITY AND MORTALITY WEEKLY REPORT 30: 305 (1981).
4. MORBIDITY AND MORTALITY WEEKLY REPORT 31: 365 (1982).
5. MORBIDITY AND MORTALITY WEEKLY REPORT 31: 577 (1982).