NORFOLK, VA. - DNA markers from the cauliflower mosaic virus (CaMV 35S DNA) can serve as safe, surrogate indicators of both direct and indirect transmission pathways of nosocomial pathogens in a neonatal intensive care unit (NICU), according to the results of a pilot study.
With these results validating the need for further investigation, researchers intend to legitimize the markers as useful tools for evaluating baseline data and designing educational interventions for reducing nosocomial infections in the NICU.
"We want to develop a confidence about just how predictably this marker will spread given the way we currently do things. What we would then like to do is to develop various strategies to reduce the transmission, to promote hand washing, and then, using the probe as a marker, to show that the transmission has decreased," said David G. Oelberg, MD, director of the division of neonatal medicine, Eastern Virginia Medical School, Norfolk, VA, and a co-researcher in the study.
While the researchers conceded that transmission does not equate with infection, the intent of these early studies is to establish baseline recoveries and transmission pathways of the DNA probe. The advantages of using the markers are that they are safe, noninfectious, do not replicate in the environment and do not require an outbreak to evaluate transmission routes, as confirmed by previous studies, Oelberg said.
The researchers' findings were based on their study of the spatial and temporal recovery of the surrogate DNA marker in the environment and hands in a NICU that included six patient-care pods, each of which housed from four to six infants and its own central charting area. The marker was placed on the telephone handle in only one of the six NICU pods and the telephone was not cleaned for the duration of the study.
Thirty-two samples were collected from predetermined sites within each pod at zero, four, eight, 24 and 48 hours and seven days after DNA placement. Samples were also collected from areas of the NICU which were not associated with direct patient care, including the staff break room and resident physician charting area. Polymerase chain reaction (PCR) was used to detect the markers, which allowed for the identification of as little as one DNA molecule per sample.
Analysis of positive sample sites by patient care pod, without regard to type or time of sample collection, showed that 58% of all samples collected throughout seven days from the study pod were positive. By contrast, a mean of 18% of samples from the remaining five pods were positive throughout the same period.
After introduction, the marker was distributed widely within the designated pod within four hours, with the highest rates occurring on staff hands and on charts in the central charting area. Throughout the subsequent 44 hours, recovery rose for equipment and bedside sites and declined for hands. These observations suggest that the probe was transmitted by hands early in the study and from the charting area to other sites within the pod during the first 48 hours of probe placement, according to the researchers.
In an unexpected finding, the researchers identified a relatively high percentage of positive sample sites from areas outside the patient-care pods, with the highest percentage in the resident physicians' charting area at 80% positive. In addition, sample sites from the staff break room, central nursing station and female staff changing room were positive 30% to 50% of the time. The researchers attributed these high recovery rates to the indirect transfer of the DNA probe by a caregiver to an inanimate surface or fomite in these areas, which provided opportunity for inoculation or reinoculation of uncontaminated caregivers.
Further research based on this pilot study is intended. In addition, related ongoing study indicates positive correlation for simultaneous transmission of both marker and bacteria as well as for marker and virus, a factor that may be underestimated in nosocomial infection in the NICU.
"I think a future area in the NICU will be to try to track down the viral pathogens, which I suspect might play as big a role in our population as bacterial pathogens," Oelberg said.
For more information:
- Oelberg D, Joyner S, Jiang X, et. al. Detection of pathogen transmission in neonatal nurseries using DNA markers as surrogate indicators. Pediatrics 2000;105;311-315.
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