In March 1992, a community investigation of nine acute Plasmodium falciparum malaria cases in Riyadh children revealed no recent travel, blood transfusion or anopheline exposure. Hospital admission in the month prior to malaria onset proved to be the only common risk factor. We began an investigation in one 352-bed pediatric hospital to determine the mode of transmission and to prevent more cases.
Methodology
We reviewed hospital records to identify all confirmed malaria from January through April 1992. We interviewed parents and reviewed medical records for travel, blood transfusion, prior admission, room location and parenteral therapy. We compared these exposures with those of surveys of the general patient population. We questioned mothers who stayed continuously in the patients' rooms, nurses and other hospital staff about recent malaria or prolonged febrile illness and exposure to mosquitoes. We used light traps for anopheline capture. We observed and questioned nurses about administration of parenteral drugs and reviewed their schedules in relation to malaria cases.
Results
We identified 41 acute falciparum malaria cases; 51% (21) had not left Riyadh (local cases). All local cases were in a hospital for another illness in the month before malaria onset (exposure admission) compared with 25% of the general patients in the month before their current illness (p<0.0005; Fisher's exact test). We detected no malaria in mothers or hospital staff. We captured only Culex mosquitoes. For each exposure admission the hospital room was shared or next to one with one or more patients with P. falciparum trophozoites (source case), compared with 30% of 60 admissions of randomly selected patients (p<0.001; Fisher's exact test). In their exposure admission, 90% of the local cases had a heparin lock, compared with 49% of the patient survey (p<0.002; Fisher's exact test). During the exposure admission of each local case a corresponding source case also had a heparin lock. Nurses flushed heparin locks with needleless syringes that had visible blood in them after use. In anonymous questionnaires, 10% of nurses answered that they reused needle-less syringes on cannulas and intravenous lines. Nurses more often assigned to exposure admissions had the lowest level nursing degrees. As soon as we began questioning nurses about heparin locks, exposure of new local cases ceased.
Conclusion
Falciparum malaria was transmitted between patients when syringes for flushing heparin locks were used in sequential patients. This practice could transmit other bloodborne diseases.