Pulsed field gel electrophoresis of Haemophilus influenzae type b (Hib) isolates from blood culture of two elderly nursing home residents (lanes 1 and 2) compared with epidemiologically unrelated H. influenzae isolates sent to our laboratory for typing: lane 3, laboratory Hib strain; lane 4, non-H. influenzae; lane 5 and 12, invasive nontypeable H. influenzae; lane 6-11, unrelated Hib isolates; lane 13, H. influenzae type a; lane 14, 1 kilobase molecular marker. The enzyme used for DNA digestion