Fig. 6. Bacterial conjunctivitis in a hospital-based, long-term care facility. The monthly threshold levels for 1990 and for 1992 shown were calculated from endemic rates over the corresponding previous 2 years. (Mylotte JM: Analysis of infection control surveillance data in a long-term care facility: Use of threshold testing. Infect Control Hosp Epidemiol 17: 101, 1996)