Susan M. Harrington

Surveillance strategies and impact of vancomycin-resistant enterococcal colonization and infection in critically ill patients

ObjectiveTo determine the optimal site and frequency for vancomycin-resistant enterococci (VRE) surveillance to minimize the number of days of VRE colonization before identification and subsequent isolation. Summary Background DataThe increasing prevalence of VRE and the limited therapeutic options for its treatment demand early identification of colonization to prevent transmission. MethodsThe authors conducted a 3-month prospective observational study in medical and surgical intensive care unit (ICU) patients with a stay of 3 days or more. Oropharyngeal and rectal swabs, tracheal and gastric aspirates, and urine specimens were cultured for VRE on admission to the ICU and twice weekly until discharge. ResultsOf 117 evaluable patients, 23 (20%) were colonized by VRE. Twelve patients (10%) had VRE infection. Of nine patients who developed infections after ICU admission, eight were colonized before infection. The rectum was the first site of colonization in 92% of patients, and positive rectal cultures preceded 89% of infections acquired in the ICU. This was supported by strain delineations using pulsed-field gel electrophoresis. Twice-weekly rectal surveillance alone identified 93% of the maximal estimated VRE-related patient-days; weekly or admission-only surveillance was less effective. As a test for future VRE infection, rectal surveillance culture twice weekly had a negative predictive value of 99%, a positive predictive value of 44%, and a relative risk for infection of 34. ConclusionsTwice-weekly rectal VRE surveillance of critically ill patients is an effective strategy for early identification of colonized patients at increased risk for VRE transmission, infection, and death.

Linezolid-resistant Staphylococcus aureus in two pediatric patients receiving low-dose linezolid therapy.

We report 2 sisters with hyper-IgE syndrome treated with daily suppressive dosages of linezolid (LZD) who developed LZD-resistant Staphylococcus aureus carrying the G2576T mutation in the 23S rRNA gene. Molecular typing suggested transmission of the resistant strain from one sister to the other. LZD-susceptible S. aureus was isolated 2 months after LZD discontinuation. LZD-resistant S. aureus remains rare but may occur while receiving suppressive therapy.

Automated and Manual Methods of DNA Extraction for Aspergillus fumigatus and Rhizopus oryzae Analyzed by Quantitative Real-Time PCR

ABSTRACT Quantitative real-time PCR (qPCR) may improve the detection of fungal pathogens. Extraction of DNA from fungal pathogens is fundamental to optimization of qPCR; however, the loss of fungal DNA during the extraction process is a major limitation to molecular diagnostic tools for pathogenic fungi. We therefore studied representative automated and manual extraction methods for Aspergillus fumigatus and Rhizopus oryzae. Both were analyzed by qPCR for their ability to extract DNA from propagules and germinated hyphal elements (GHE). The limit of detection of A. fumigatus and R. oryzae GHE in bronchoalveolar lavage (BAL) fluid with either extraction method was 1 GHE/ml. Both methods efficiently extracted DNA from A. fumigatus, with a limit of detection of 1 × 102 conidia. Extraction of R. oryzae by the manual method resulted in a limit of detection of 1 × 103 sporangiospores. However, extraction with the automated method resulted in a limit of detection of 1 × 101 sporangiospores. The amount of time to process 24 samples by the automated method was 2.5 h prior to transferring for automation, 1.3 h of automation, and 10 min postautomation, resulting in a total time of 4 h. The total time required for the manual method was 5.25 h. The automated and manual methods were similar in sensitivity for DNA extraction from A. fumigatus conidia and GHE. For R. oryzae, the automated method was more sensitive for DNA extraction of sporangiospores, while the manual method was more sensitive for GHE in BAL fluid.