abdominal pain , emesis , and a high fever developed in patient 1 , a 9-year - old gambian boy with sickle cell disease residing in the united states , during the flight home after a month in the gambia ; he had taken no malaria prophylaxis drugs . after diagnosis of p. falciparum malaria with 4% parasitemia and transfer to unit a of a tertiary care hospital , he responded well to antimalarial therapy and was discharged 2 days later . seven days before patient 1 's admission , patient 2 , a 14-year - old girl , with severe developmental delay , was admitted to unit a for placement of a surgical feeding tube . chart review and interviews indicated that neither patient had glucose monitoring by glucometer , blood transfusions , common infusions such as contrast material , or a needlestick injury report , all events that have been previously implicated in nosocomial malaria . medicine doses given and blood samples drawn were documented with a separation time > 50 minutes . a week after discharge and 17 days after sharing the semiprivate room , patient 2 was admitted to another hospital ( 3-day stay ) , and a viral illness was diagnosed after all cultures were negative for pathogens . persistent fever and pancytopenia developed and resulted in her readmission to unit a of the tertitary care hospital , now 23 days after sharing the room with patient 1 . patient 2 was febrile and pale , with no notable change in her baseline neurologic state . the leukocyte count was 1,890 cells / mm , hematocrit was 35.2% , platelets were 47,000/mm , and total bilirubin was 1.5 mg / dl . despite administration of antimicrobial drugs for presumed microbial sepsis , the following conditions developed over the next 72 hours : persistent spiking fevers ; loose , nonbloody stools ; splenomegaly ; abdominal distension ; and bilateral lower extremity edema . formal review of her peripheral blood smear by the hematology consultation service showed intraerythrocytic ring forms indicative of p. falciparum malaria , with 12% parasitemia and 200 gametocytes / mm . after 3 blood transfusions and quinidine gluconate and doxycycline therapy , the patient was discharged on hospital day 14 , with a stable hematocrit , persistent gametocytemia , and splenomegaly . the patient lives with her parents in the baltimore - washington area 12 miles from the nearest international airport . she had no history of recent travel to any areas that are endemic for malaria . approval for the study was obtained from johns hopkins university two potential sources of nosocomial transmission in unit a were identified : 1 ) heparin syringes , which were filled from multidose vials , and 2 ) factory preloaded 10-ml saline flushes , of which up to 3 ml was used per flush for intravenous lines not in use . hospital policy had strict guidelines for using multidose devices and did not allow reusing single use devices . however , interviews of 7 nurses , including those who cared for the 2 patients , showed that 2 nurses admitted reusing saline flushes on the same patient , and 4 nurses had observed saline flushes being reused in unit a. reusing multidose heparin vials was not documented . to determine whether used saline flush syringes that were visibly clear contained blood , we tested saline from 8 used syringes and 2 unused controls . after the contents were centrifuged to concentrate erythrocytes , blood was found in 4 of 8 of the used syringes ( figure 1 ) by using matrix - assisted laser desorption ionization / time - of - flight mass spectrometry ( 7 ) . matrix - assisted laser desorption ionization detected the  and  chains of hemoglobin as the ions at mass / charge ( m / z ) 15,126 and 15,867 , respectively , in samples a ( red ) , b ( green ) , c ( blue ) , and j ( aqua ) that were absent in the matrix alone ( black ) . the lower limit of sensitivity with matrix - assisted laser desorption ionization is 0.5 erythrocytes per ml . polymerase chain reaction ( pcr ) amplification of p. falciparum genomic dna , isolated with dnazol ( invitrogen , carlsbad , ca , usa ) , was successful from the archived giemsa blood films from both patients and 2 other patients ( not related in time or travel history ) infected with p. falciparum malaria seen at our institution in the past year . figure 2 shows that the pcr product restriction digests for the polymorphic p. falciparum merozoite protein 2 ( pfmsp2 ) ( 8) and the p. falciparum chloroquine resistance transporter ( pfcrt ) ( 9 ) gene fragments were identical for patients 1 and 2 . patient 1 and 2 are identical at the polymorphic pfmsp2 ( lanes 1 and 2 ) , while unrelated patient controls ( lanes 3 and 4 ) are different . genomic dna from clone hb3 ( lane 6 ) and isolate nf54 ( lane 7 ) are also included as additional positive controls . we also examined 4 p. falciparum microsatellite alleles ( ta81 , pfpk , c13m30 , c4m8 ) at independent chromosomal loci by a fluorescent - tagged heminested pcr amplification ( 10 ) . patients 1 and 2 had identical plasmodium microsatellite lengths at all 4 loci ; each of the positive controls was different as shown in figure 2 , the figure a1 , and the table . with the simplistic assumption of 10 alleles at each microsatellite loci and pfmsp2 , the chance occurrence of identity is < 1:100,000 . by using the ampflstr profiler kit ( applied biosystems , foster city , ca , usa ) , subsequent forensic analysis of the human genomic dna from leukocytes in the same isolated p. falciparum dna samples from the blood films demonstrated the sex difference between patients 1 and 2 . the analysis also demonstrated the differences at 9 human microsatellite loci , which indicated that cross - contamination during processing was not a likely source for the similarities detected . natural transmission of malaria between patients 1 and 2 by a mosquito is not possible within 24 hours ; the maturation cycle from ingestion of viable gametocytes in a blood meal to infective sporozoite stage in the mosquito salivary glands is 835 days ( 11 ) . direct mechanical transmission of parasitized blood by an arthropod vector is a theoretical possibility , but no such transmission has ever been reported , and the female anopheles mosquito does not regurgitate blood upon refeeding . another remote possibility , luggage malaria , is the introduction of an already infectious mosquito from the gambia brought into unit a through patient 1 's luggage ( 12 ) . if this were the case , a different parasitic genotype would be expected in patients 1 and 2 because the wild mosquito that infected patient 1 , from 1 to 2 weeks before onset of symptoms , would have died 26 days after delivering the infective bite . likewise , an asymptomatic traveling companion of patient 1 would have a distinct parasite genotype . in this report potential sources not excluded were multidose heparin vials and saline flush syringes . however , identifying reuse of saline flush syringes in the unit and detecting blood in clear , used saline flush syringes suggested that this was the most likely source . finally , molecular identity of p. falciparum isolated from patients 1 and 2 , as assessed by restriction fragment length polymorphism of pfmsp2 , and forensic microsatellite analysis of p. falciparum genotypes confirmed that contaminated fluid from patient 1 was the source of the infection in patient 2 . together , these data strongly suggest that apparently clear solution in a used saline flush syringe containing infected p. falciparum erythrocytes , was reused on a neighboring patient , leading to nosocomial transmission of malaria . saline flush vials and bags have been implicated in nosocomial transmission of hepatitis b and microbes , respectively ( 13,14 ) . theoretically , a single infected erythrocyte is able to transmit malaria by inoculation . patient 1 had almost 200 million infected erythrocytes per milliliter of blood based on parasitemia level . based on our data , therefore a single microliter of patient 1 's blood diluted into 5 ml of saline would be almost 40,000 infected erythrocytes per milliliter of an apparently clear solution . our report illustrates that nosocomial transmission can occur in a tertiary care setting in the united states , despite healthcare workers ' access to gloves , disposable needles , intravenous devices , and flushes . the common perception that flushing practices are not associated with the aspiration of minute amounts of blood contributed to this occurrence of nosocomial malaria . our institution , like many others , has used such episodes to facilitate change and refocus on patient safety . the interventions initiated specifically included retraining of pediatric staff about 1 ) no reuse of single use saline flushes , 2 ) transmission of bloodborne pathogens with an emphasis on nonviral pathogens , and 3 ) removal of multidose vials , including those with heparin , from pediatric units . warnings about the potential risks of reusing saline flush syringes have been incorporated into institution - wide safety training . ongoing rigorous review of healthcare practices and strict adherence to body and fluid precautions are essential for minimizing patient exposure to highly infectious pathogens , even in resource - rich settings .
an investigation of malaria in a us patient without recent travel established plasmodium falciparum molecular genotype identity in 2 patients who shared a hospital room . 
 p. falciparum can be transmitted in a hospital environment from patient to patient by blood inoculum if standard precautions are breached .