Detection of viable antibiotic-resistant/sensitive Acinetobacter baumannii in indoor air by propidium monoazide quantitative polymerase chain reaction.

Acinetobacter baumannii represents a significant cause of nosocomial infections. Therefore, we combined real-time quantitative polymerase chain reaction (PCR) with the propidium monoazide (PMA-qPCR) to assess the feasibility of detecting viable, airborne A. baumannii. The biological collection efficiencies of three samplers for collecting airborne A. baumannii were evaluated by PMA-qPCR in a chamber study. After sampling, the effects of storage in collection fluid on A. baumannii were evaluated. The results showed that the culturable ratio of A. baumannii measured using the culture method was significantly correlated with the viable ratio measured using PMA-qPCR, but was not significantly correlated with the qPCR results. It was indicated that the AGI-30 impinger and the BioSampler were much more effective than the Nuclepore filter sampler for collecting airborne A. baumannii. The storage temperature was critical for aerosol samples, as the loss of viable A. baumannii was minimized when the PMA-bound DNA was stored at -20°C or if the collected cells were stored at 4°C and subsequently processed by PMA-qPCR within 1 month. The PMA-qPCR method was also to distinguish between colistin-sensitive and colistin-resistant A. baumannii, and no colistin-sensitive A. baumannii was detected by PMA-qPCR upon treatment of the BioSampler collection medium with 2 µg/ml colistin for 5 min.

Seasonal influences on childhood lead exposure.

We conducted a study to examine seasonal changes in residential dust lead content and its relationship to blood lead in preschool children. We collected blood and dust samples (floors, windowsills, and carpets) to assess lead exposure. The geometric mean blood lead concentrations are 10.77 and 7.66 microg/dL for the defined hot and cold periods, respectively (p < 0.05). Lead loading (milligrams per square meter) is the measure derived from floor and windowsill wipe samples that is most correlated with blood lead concentration, whereas lead concentration (micrograms per gram) is the best variable derived from carpet vacuum samples. The variation of dust lead levels for these three dust variables (floor lead loading, windowsill lead loading, and carpet lead concentration) are consistent with the variation of blood lead levels, showing the highest levels in the hottest months of the year, June, July, and August. The regression analysis, including the three representative dust variables in the equations to predict blood lead concentration, suggests that the seasonality of blood lead levels in children is related to the seasonal distributions of dust lead in the home. In addition, the outdoor activity patterns indicate that children are likely to contact high leaded street dust or soil during longer outdoor play periods in summer. Consequently, our results show that children appear to receive the highest dust lead exposure indoors and outdoors during the summer, when they have the highest blood lead levels. We conclude that at least some of the seasonal variation in blood lead levels in children is probably due to increased exposure to lead in dust and soil.

The effectiveness of a home cleaning intervention strategy in reducing potential dust and lead exposures.

The changes in dust loading, lead loading and lead concentration, determined from vacuum samples and wipe samples collected during the Childhood Lead Exposure Assessment and Reduction Study (CLEARS) were analyzed to determine the efficacy of the cleaning protocol in homes of children found to have moderate lead poisoning, e.g. levels between 10-20 micrograms/dL. The samples were collected at least twice, and in 65 homes three times, during the course of a year long intervention in homes where half were randomized into a group which received a standardized Lead Intervention program for lead reduction, and the other homes only received an Accident Intervention program. The homes with lead burdened children were located in Hudson County, New Jersey (primarily in Jersey City), and were referred to the CLEARS by a number of private and public sources. Each home had wipe sampling conducted with the LWW Sampler (patented), and vacuum sampling was completed using a device described by Wang et al. in Applied Occupational and Environmental Hygiene. The results were compared in two ways: (1) between the two intervention groups, and (2) over the time course of the intervention period. When compared to the values seen in the first visit vacuum sampling results showed statistically significant decreases in lead loading and dust loading by the third sampling visit for the Lead Intervention homes. Substantial reductions in lead loading and dust loading were also seen when the Lead Intervention values were compared to values obtained in the Accident Intervention homes over the course of the year long intervention. The wipe sampling results for the 65 homes with three visits found no significant reductions in dust loading and lead loading among any of the room surfaces sampled in the Accident Intervention homes. There were 75% and 50% reductions observed on the window sills and on the bedroom floors of the homes which participated in the Lead Intervention. The levels in the living room and the kitchen showed very little change in loadings. This appeared to be due to the fact these rooms were near a background or baseline value of 0.3 g/cm2 and 0.12 mg/cm2 for dust loading and lead, respectively. This was substantiated by the window sills and bedroom wipe sampling results since each surface approached these values by the third visit. Significant reductions in lead concentrations found in the wipe samples from the intervention homes appeared to be related to the absence of historically active sources of lead in these homes, rather than elimination of current sources. The results of the micro-environmental sampling program in CLEARS indicated that a year long cleaning protocol can significantly decrease lead levels in rugs and on other exposed surfaces. This will reduce the potential for exposure to lead among the occupants, especially children, that come in contact with such surfaces.

A field comparison of two methods for sampling lead in household dust.

Comparability of dust lead measurements has been a difficult problem due to different sampling and analysis techniques. This paper compares two dust sampling techniques, the U.S. Department of Housing and Urban Development (HUD) dust wipe method and the Lioy, Wainman, Weisel (LWW) sampler. The HUD method specifies using a moist towelette to pick up as much dust as possible in a specified area and estimates total lead loading. The LWW sampler collects the dust on preweighed wetted filter media, and provides greater standardization of the sampling path and pressure applied. LWW samples were analyzed using inductively coupled plasma mass spectronomy (no samples below minimum detection limit), while HUD samples were analyzed using flame atomic absorption (32% of samples below minimum detection limit). A bootstrapping technique was used in the analysis to contend with those HUD samples below the minimum detection limit. Mixed model equations were generated to predict HUD values from LWW results, and to examine the effects of sampling location, time, and method. The results indicate that the two samplers performed similarly under field conditions, although the LWW sampler produced consistently lower lead loading estimates. LWW values that predicted HUD lead clearance values of 100 micrograms/ft2 for floors and 500 micrograms/ft2 for window sills were 72 micrograms/ft2 and 275 micrograms/ft2, respectively. To examine internal reproducibility, duplicate samples were taken using both the HUD and LWW methods. Correlation results within paired samples indicated a statistically significantly higher (p < 0.001) internal reproducibility for lead loading, for the LWW sampler (r = 0.87), than for the HUD method (r = 0.71). Some of the differences appeared to be related to the analytical methods.