Antimicrobial Stewardship and Infection Control: August 2018

Prior ESBL infection or fecal carriage increases future ESBL infection risk, but by how much? In this study, Lindblom et al reviewed all inpatient and outpatient blood, urine, and fecal screening cultures positive for ESBL-producing Enterobacteriaceae (EPE) at a microbiology lab serving a large metropolitan area in Sweden over a ten-year period. For each patient’s initial EPE-positive culture, the subsequent clinical cultures over a minimum follow-up period of 1 year (mean duration of follow-up 3.7 years) were examined for the presence of EPE. There’s some unclear wording in the methods here– the authors write they examined the “first and last” cultures, but later context suggests they mean the first and last EPE-positive cultures.

Anyway, a total 3272 patients had at least one EPE-positive sample; of these, EPE was most often first detected in urine (n=1717) or on fecal screen (n=1717); in only 119 cases (4%) did a patient have ESBL bacteremia without a prior positive urine or fecal screening culture. Most patients did not have a subsequent EPE-positive clinical culture (94% for urine, 72% for fecal, and 71% for blood), though subsequent positives were more common in patients whose first EPE was isolated in a clinical culture versus a fecal screen (28% vs 5.6%). Patients whose first EPE-positive was a fecal screening culture had their last EPE-positive culture a median 6.4 months later, and only 1.4% had an EPE-positive clinical culture after one year.

For patients whose first EPE-positive culture was from urine, the median time to the final EPE-positive culture was 5.3 months and only 1.6% had a subsequent EPE-positive blood culture. Predictors of recurrent EPE infection included age >65 years, male sex, and infection with ESBL K. pneumoniae versus ESBL E. coli. Of the patients whose first documented EPE was a bacteremia, 67% were over 65 years of age and 45% had a concurrent EPE-positive urine culture. The median time to last EPE-positive culture in this group was 2 months; recurrent EPE infections after 9 months were rare and occurred only in the elderly.

This study tells us a few things that can help guide empiric gram-negative antibiotic therapy. First, the large majority of patients with an ESBL bacteremia have had a prior EBSL-positive culture (even of you omit the fecal screening cultures, which aren’t routinely done in my neck of the woods, only 6.4% of the first EPE-positive cultures were from blood). Second, when a patient does show up with an ESBL bacteremia out of the blue, they are usually elderly and/or have a urinary focus of infection. Third, the “half-life” of ESBL carriage seems to be a couple of months, with recurrent ESBL infection after 6-12 months of no ESBL-positive cultures being rare. 29796984

Amoxicillin is not much better than placebo for lower respiratory tract infection unless a mixed bacterial and viral infection is present. This is a secondary analysis of the GRACE trial, which showed no convincing benefit for amoxicillin treatment of LRTIs as a whole. In that RTC, adults showing up to clinic with acute cough and no suspected pneumonia were randomized to either 1g amoxicillin or placebo three times a day for 7 days. Respiratory samples were tested for bacterial and viral pathogens, and the patients were asked to keep a symptom diary and rate their symptom severity on a 6-point scale. In this study, the authors stratified the patients’ responses to amoxicillin or placebo by whether they had a bacterial pathogen, viral pathogen, or both isolated from their respiratory sample.

The study randomized 2058 patients, of whom the majority (87-88%) provided complete symptom journals. Amoxicillin did not reduce symptom duration in any group. In patients with a purely bacterial infection, amoxicillin was associated with a trivial decrease in patient-assessed symptom severity (0.26 points on a 6-point scale). In patients with a mixed bacterial and viral infection, amoxicillin was associated with a lower rate of illness deterioration, defined as return to clinic with new or worsening symptoms or hospitalization within the following month (10% vs 32% with placebo, p<0.001). Elevation of PCT, CRP, and BUN failed to predict benefit from amoxicillin versus placebo.

Using the numbers presented in Table 3 (which included the proportion of mixed bacterial and viral infection in the cohort), I calculated the number needed to treat for a course of amoxicillin to prevent one illness deterioration in LRTI as ~46. I don’t know about you, but prescribing 322 days of amoxicillin to prevent one return to clinic sounds like a bad deal to me. 29108950

Can BETR disinfection of patient rooms prevent acquisition of nosocomial pathogens? This study was a prespecified secondary analysis of the BETR Disinfection study, a crossover cluster-randomized trial looking at different methods of terminal disinfection of patient rooms across 9 US hospitals. The enhanced disinfection methods were used in rooms that had housed patients with C. difficile, MRSA, VRE, or MDR Acinetobacter, and the methods used included standard (ammonium disinfectant, substituted with bleach for rooms with C. difficile), standard plus disinfecting UV light, bleach for all rooms, and bleach + UV light for all rooms. The outcomes of interest were hospital-wide incidences of all the mentioned target organisms, both individually and as a group. Each strategy was used for 7 months with a 1-month wash-in period.

The study captured a total 271,740 patients with 2,681 nosocomial acquisitions of target organisms across 375,918 admissions. The incidence of all organisms collectively was not affected by the type of disinfection method used; however, the standard + UV light method was associated with lower incidence of C. difficile (RR 0.89; p=0.031) and VRE (RR 0.56; p=0.048).

Those are some pretty borderline p values, but the finding is plausible, and I suppose a 10% reduction in nosocomial transmission of C. difficile might be worth investing in one of those weird little UV light Daleks if your hospital has a significant problem with CDI. What do you think? 29880301

Speaking of C. difficile, this month's issue of OFID reports the sensitivity and specificity of two rescue dogs trained to sniff out fecal samples containing toxigenic C. difficile. Using canines as diagnostic tools is not a bad idea – several species have olfactory senses dramatically better than our own, and dogs have been successfully trained to reliably detect other organisms (e.g. bed bugs) in the past. These dogs were trained using clinical stool samples and then tested against a battery of 300 additional clinical samples, with positive stools defined as both a positive glutamate hydrogenase EIA and a positive C. difficile PCR and negative stools defined as a negative PCR. Figures 1 and 2 are so adorable that I wonder if this whole study was an excuse to get dog pics into the medical literature. The pups detected C. difficile-positive samples with sensitivities of 78% and 93% and specificities of 84% and 85% (PPV 45-50% and NPV 96-99%). Intercanine reliability was moderate, which would make the widespread adoption of dogs as C. difficile diagnostic tools impractical. So, your hospital microbiology lab is unlikely to have a K9 unit any time soon. 30151408