RESULTS

The US Customs and Border Protection had no documented recent international travel for patient 1; her last known travel was to Trinidad in 2006. No evidence of local mosquito transmission or overwintering mosquito activity was detected within patient 1’s residence or in hospital B. She spent limited time outside the group home, her residence was not located near any airport, and she had no history of visitors who had traveled, eliminating the possibilities of “airport” and “baggage” malaria.Reference Isaacson ^{8 ,} Reference Castelli, Cabona, Brunori and Carosi ⁹ There was no history of intravenous drug use.

Patient 1 did not receive blood products during her time at either hospital. Her cholecystectomy followed a child’s circumcision as the second surgical procedure of the day at hospital B. Review of medical records for patients hospitalized at the same time and on the same floor at hospital B identified a 42-year-old woman (patient 2) who was admitted with fever and abdominal pain on the same day as patient 1. Patient 2 had returned from a 20-day trip to Nigeria and denied taking malaria chemoprophylaxis. Blood smears collected from patient 2 on February 16 and 18, 2012, were considered negative and positive, respectively, for the presence of malaria-like parasites. Though hospital laboratory protocol required the positive specimen be referred to a commercial laboratory for additional testing, the specimens were not sent. Consequently, the species of malaria was not identified during her hospitalization. The patient was treated with mefloquine for presumed P. falciparum infection. Because the malaria diagnosis was not confirmed, the case was not reported to the Department of Health and Mental Hygiene. Since January 1, 2012, hospital B had reported only 1 case of malaria, diagnosed 4 weeks before patient 1’s hospitalization.

Investigation at hospital B revealed patients 1 and 2 were simultaneously in the emergency department on February 16, 2012, but were cared for in different areas by different staff. The site investigation identified no infection control breaches in the emergency department, and all staff interviewed reported that the only common medication, sterile saline for injection, would have been obtained from different areas and administered by different staff. All staff reported intravenous fluid bags and tubing sets are never shared, and intravenous bags are not prepared (“pre-spiked”) in advance of their use.

Patients 1 and 2 were admitted to the same inpatient unit in hospital B and, for a week, resided in nearby rooms. While on the unit, patients 1 and 2 were cared for by common staff and underwent diagnostic phlebotomy; however, medical records indicated that different phlebotomists drew blood from each patient at different times. Individual saline syringes were used for flushing intravenous lines. Both patients may have received fingerstick blood glucose monitoring, but the medical record was inconsistent for patient 2. Staff reported that glucometers were not consistently cleaned and disinfected after each use.

P. falciparum was confirmed for patients 1 and 2. A blood smear collected from patient 2 on February 16, 2012, initially considered negative by light microscopy at the hospital laboratory, revealed P. falciparum on repeat light microscopy and by real-time polymerase chain reaction. P. falciparum specimens from both patients were identical at the 12 microsatellite loci tested, with the exception of 1 minor allele of a microsatellite marker that was detected in patient 2’s but not in patient 1’s specimen. They also had identical mutations identified by pyrosequencing at 10 positions in 3 genes associated with drug resistance; the pattern of mutations was consistent with P. falciparum of African or Asian, and not South American, origin.Reference Gbotosho, Folarin and Bustamante ¹⁰ The microsatellite analysis at 12 loci, along with the pyrosequencing results, indicated the parasites from the 2 patients were genetically identical.