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October 2009
Vol. 19 No. 10
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IDSA Journal Club
October 2009

Preventing Influenza: A Comparison of Surgical Masks and N95 Respirators
Reviewed by Nina Kim, MD

Influenza can be transmitted by contact or inhalation of droplets and smaller aerosol particles. The relative contribution of each mode has not been well characterized, and clinical trials examining preventive strategies have been few. A multicenter Canadian study published online in the Journal of the American Medical Association on Oct. 1 sought to address whether N95 respirators are superior to standard face masks in preventing the transmission of influenza among health care workers.

The investigators randomized 478 nurses from emergency departments and medical or pediatric wards from eight hospitals to wear either surgical masks or N95 respirators. The nurses were then followed from January to April 2009 to track influenza infection. The primary outcome was laboratory-confirmed influenza by either detection of viral RNA using PCR from a nasal or nasopharyngeal swab, or at least a four-fold increase in serum antibodies to circulating influenza strain antigens.

Fifty cases of infection were found in the surgical mask group (23.6 percent) compared with 48 in the N95 respirator group (22.9 percent) (absolute risk difference -0.73%, P=0.86). Interestingly, only a minority of these were confirmed by symptom-prompted PCR detection (2.8 percent among surgical mask users versus 1.8 percent among N95 respirator users), and the vast majority were diagnosed by serologic confirmation. No differences were seen in the subset of novel H1N1 cases (8 percent versus 11.9 percent, P=0.18). Of note, only 29 percent of the nurses were vaccinated against seasonal influenza. The authors concluded that surgical masks were not inferior to N95 respirators for preventing influenza.

This study suggests that surgical masks may be sufficient for prevention of influenza transmission in acute care settings. However, the research was limited in its characterization of exposure risks (e.g., frequency of exposure to aerosol-generating procedures) and distribution of these risks between these intervention groups. Perhaps more importantly, the study reminds us of the unacceptably low vaccination rates among health care workers, the alarmingly high rate of asymptomatic or minimally symptomatic influenza, and the necessity of a multifaceted approach when it comes to protecting our patients.

(Loeb et al. JAMA. 2009;302(17): E-pub)

Inactivated Vs. Live Attenuated Influenza Vaccine: Which is More Effective in Adults?
Reviewed by Jason Weinberg, MD

Inactivated influenza vaccine was more effective than the live attenuated form of the vaccine in adults during 2007-2008 influenza season, according to a report in the Sept. 24 issue of the New England Journal of Medicine. The implications of these findings for vaccines for novel influenza A (H1N1), however, remain to be seen. 

The report’s authors enrolled 1,952 adults in a randomized, double-blind, placebo-controlled trial to evaluate the effectiveness of inactivated and live attenuated influenza vaccines. No serious adverse events were attributed to either vaccine during the study. Both vaccines provided some protection against laboratory-confirmed, symptomatic influenza infection, the study’s primary end point. Absolute efficacy against influenza A and B strains was 68 percent for the inactivated vaccine and 36 percent for the live attenuated vaccine. There was a 50 percent reduction in laboratory-confirmed influenza among inactivated vaccine recipients compared with those who received the live attenuated vaccine. Similar absolute and relative efficacies were noted when the analysis was restricted to influenza A, which comprised the majority of influenza cases during the study season.

As the authors speculate, the differences between the vaccines may stem from immune responses to previous influenza strains that cross-react with the vaccine strain and limit its replication. The findings, however, are likely not relevant to all scenarios. For instance, other studies have shown that live attenuated vaccine is more efficacious than inactivated vaccine in children. In addition, it is not yet clear how these findings will relate to vaccines for the novel H1N1 strain, in which a lack of substantial pre-existing cross-protective immune responses to the novel influenza strain may result in similar efficacies for inactivated and live attenuated vaccines. In all cases, continued surveillance will be essential to guide vaccine development and implementation moving forward.

(Monto et al. N Eng J Med 2009;361:1260-7)

Using Procalcitonin Levels to Guide Antibiotic Use in Patients With Lower Respiratory Tract Infections (LRTI)
Reviewed by Rachel Simmons, MD

Appropriate use of antibiotics in LRTI continues to be a challenge for health care providers. Some patients clearly benefit from antibiotics, but overuse contributes to antimicrobial resistance in the community and causes medication-related side effects in some individuals.

An article and accompanying editorial in the Sept. 9 issue of the Journal of the American Medical Association discuss the findings of a multi-center, noninferiority randomized controlled trial using procalcitonin (PCT) levels to tailor antibiotic use in lower respiratory tract infections. The trial included 1,359 adults with LRTI enrolled from emergency departments at six Swiss hospitals. In the control group, antibiotic use was based on recent clinical guidelines. In the procalcitonin group, antibiotics were recommended or discouraged based on serum PCT levels. 

The study population was older with a mean age of 73. Two thirds of the subjects had community-acquired pneumonia, and more than 90 percent of the patients in both groups required hospital admission. The overall rate of adverse events (composite endpoint of death, ICU admission, disease-associated complications, or recurrence of LRTI) was not significantly different between the two groups (15.4 percent in the PCT group versus 18.9 percent in the control group). The overall duration of antibiotic exposure was significantly less in the PCT group compared to the control group (5.7 versus 8.7 days), and the overall rate of antibiotic-related adverse events was also reduced (19.8 percent versus 28.1 percent).

As the largest study to date examining the use of procalcitonin levels in the management of LRTI, the results suggest that a decision algorithm that incorporates rapidly available procalcitonin levels can safely reduce the use of antibiotics in LRTI.  Whether such a computer-based algorithm could be easily operationalized in different clinical settings remains to be studied.

(Schuetz et al. JAMA 2009;302(10):1059-1056 and Yealy et al. JAMA 2009 302(10):1115-1116)

Soap and Water Appears Best for Eradicating Clostridium difficile from Hands
Reviewed by Sara Cosgrove, MD

Washing your hands with good old soap and water is superior to alcohol-based hand rubs for removing C. difficile, according to a study in the October issue of Infection Control and Hospital Epidemiology.

In an experimental model, the hands of 10 volunteers were contaminated with a C. difficile strain that was spore producing but nontoxigenic using two different methods. In the whole-hand protocol, subjects placed an entire hand in a glove containing the organism. For those using the surface contamination protocol, the palm was placed on a pre-contaminated ceramic tile. The latter approach was thought to represent more closely how hands become contaminated in an actual health care setting. Volunteers cleaned their hands on different occasions with warm water with plain soap, cold water with plain soap, warm water with antibacterial soap, antiseptic hand wipes, an alcohol-based hand rub, or with nothing at all, serving as the control.

For volunteers using the whole-hand method, the largest reductions in colony counts were seen in people washing with warm or cold water and plain soap. The alcohol-based hand rub performed poorly; its effect was not statistically different from no hand hygiene at all. In the surface contamination protocol, the results were similar, with the alcohol-based hand rub again performing poorly when compared to all soap and water regimens tested.

Current hand hygiene guidelines note the potential decreased efficacy of alcohol-based hand rubs in killing C. difficile because of its lack of sporicidal activity, but few published studies to date provide evidence for this recommendation. Although this study evaluated the effectiveness of alcohol-based hand rubs in an experimental model rather than in actual clinical practice—and the study does not examine clinical outcomes such as rates of C. difficile transmission with different approaches to hand hygiene—the findings provide important evidence that using soap and water rather than an alcohol-based hand rub after caring for a patient with documented C. difficile infection should be strongly considered in clinical practice.

(Oughton et al. Infect Control Hosp Epidemiol 2009; 30:939-944)

Time to Start Talking to Mothers About Pre-mastication and HIV Transmission?
Reviewed by Christian B. Ramers, MD

Mother-to-child transmission of HIV has been thought to occur via three routes:  in utero, intrapartum, or through breastfeeding. A study in the August issue of Pediatrics suggests a novel mode of transmission—the practice of feeding infants pre-masticated food during the weaning process.

The authors describe three U.S. infants ranging in age from 9 to 35 months old who presented with clinical symptoms that prompted HIV testing. Two were born to HIV-positive mothers who were not breastfeeding, and perinatal infection was ruled out according to HIV-testing guidelines. In the third case, a great aunt involved in caring for the infant was HIV-infected, but the mother was not.  All three infants ingested food on multiple occasions that had been chewed by a caregiver infected with HIV. An investigation excluded other modes of transmission, and phylogenetic analysis of the gp41 region of env and the p17 region of gag supported pre-chewed food as the source of infection (where source case serum was available).

The significance of this novel mode of HIV transmission is unknown, but the prevalence of pre-mastication is likely greater than previously realized. The authors’ review of the limited literature surrounding this practice suggests at least 10.5 percent of caregivers pre-chew their infants’ food (range: 10.5 percent to 86.2 percent in several surveys). 

This study raises questions about the role of this practice in overall mother-to-child transmission, including in cases of so-called “late” transmission as yet attributed to breastfeeding.  While further studies are needed to quantify the risk, the authors recommend that providers discourage this practice and recommend safer feeding methods among caregivers and expecting parents who are HIV-infected or at risk of infection.

(Gauer et al. Pediatrics 2009; 124(2):658-666)

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