New evidence supports high-dose influenza vaccines

People older than 65 years are at particularly high risk for influenza-related medical complications including hospitalizations and death. In 2009, the FDA approved a trivalent inactivated vaccine with four-times the hemagglutinin antigen per strain, which was thought to improve immune response in seniors.

Background data has largely supported high-dose vaccination among seniors. In a multicenter, randomized controlled trial of high vs standard dose vaccine that included almost 32,000 patients during 2011/12 and 2012/13, 1.4% of high-dose and 1.9% standard-dose patients had an influenza-confirmed influenza-like illness, resulting in a relative efficacy of 24%. Adverse events were slightly, but significantly lower in the high-dose group but 3 high-dose recipients had serious vaccine-related events (which all resolved) vs none in the standard-dose group. A very large Medicare study during 2012/13 and 2013/14 reported similar benefits but only during 2012/13 when H3N2 was more common. Perhaps it is difficult to measure a benefit during more mild, H1N1 seasons? There have been other studies supporting the effectiveness and cost-effectiveness (at least during the 2011/12 and 2012/13 H3N2 seasons) of high-dose vaccine.

One of the larger groups of seniors in the US are patients in the Veterans Health Administration (VHA) system, so it makes sense to measure the benefits of high-dose vaccine using the VHA integrated EMR. In the June 1st JID, authors reported results of a large (industry-funded) retrospective cohort study completed using data from the 2015/16 influenza season (an H1N1 year) that included seniors with at least one inpatient or outpatient visit during the prior year (2014/15). The primary outcome was any hospitalization for pneumonia or influenza. The study used a number of nice methods to adjust for confounding including matching on baseline characteristics and the Care Assessment Need (CAN) score, that is a proxy for frailty. They also adjusted for residual confounding using the prior event rate ratio (PERR) method, which you can read more about here. Basically, PERR adjusts for outcome rates in the baseline period (before vaccination) by dividing the relative rate post-vaccination by the relative rate pre-vaccination (in the baseline period).

The final cohort (before matching) included 104,965 standard-dose and 125,776 high-dose recipients during the 2015/16  influenza season. The matched cohort had 49,091 standard-dose and 24,682  high-dose patients. Using the unmatched and matched cohorts, and using the PERR method with each, the relative vaccine effectiveness of high-dose influenza vaccine was 23% and 25%, respectively. This suggests that high-dose vaccine was effective in preventing influenza or pneumonia-associated hospitalizations among VHA patients.

These results are encouraging since they were from a more mild H1N1 season. Even more encouraging, the authors plan to automate the data extraction process and report vaccine effectiveness within 3 months of the end of each influenza season. But one note of caution, having a high-dose vaccine that is 25% more effective isn't a huge improvement, since influenza vaccines in general aren't very effective. So high-dose influenza vaccine is a small step in the right direction - but more research and new influenza vaccines are needed.

Infection Prevention Summer Reading

With apologizes to our colleagues in the Southern Hemisphere, many of us are traveling a bit this summer and are looking for good things to read. At the top of my reading list is Ed Yong's new book, "I Contain Multitudes: The Microbes Within Us and a Grander View of Life." The book by the highly regarded UK science journalist (The Atlantic, National Geographic) digs into the relationship between microbes and animals. Unfortunately, the book won't appear until August 9th, so you'll have to be a bit patient and find something else to read.

In the meantime, I've listed five recently published journal articles/studies that will hopefully tide you over until "I Contain Multitudes" appears at your bookstore.

1) A Flawed Revision of the Common Rule (Joffe and Magnus, Annals 19 July 2016). The Common Rule is the regulatory framework that guides human subjects research, think IRB. Last September, 16 federal agencies released a Notice of Proposed Rulemaking outlining proposed changes to the Common Rule. There are several potentially important changes that could negatively impact infection prevention and stewardship studies. First, the Notice seeks to redefine all research on biospecimens, including de-identified specimens, as human subject research requiring "broad consent" before storing the specimens. The discussion didn't mentioned microbiology specimens specifically, but this requirement is concerning. Second, the Notice would only exclude QI research from review if it analyzed proven interventions and limited study endpoints to utilization outcomes (e.g. cost). However, QI projects such as quasi-experimental studies of the impact of CLABSI checklists on BSI rates or mortality WOULD require IRB review and potentially individual informed consent. (Yikes!)  My sense is this could drastically curtail important research in MDRO prevention and most infection control research. Stay tuned.

2) Control of an Outbreak of Middle East Respiratory Syndrome in a Tertiary Hospital in Korea (Park GE et al. Annals, 19 July 2016). From May to July 2015, 186 confirmed cases of MERS-CoV occurred in S. Korea. The authors provide an in-depth description of a 92-person outbreak in a single tertiary-care hospital in Seoul. Interestingly, 82 of the cases occurred after exposure to a single secondary patient cared for in their emergency department. All cases were identified through contact tracing and monitoring of exposed patients and healthcare workers and all in-hospital transmission was secondary to three patients with pneumonia and productive cough. The description of events was very sobering.

3) Colonization With Methicillin-resistant Staphylococcus aureus and Risk for Infection Among Asymptomatic Athletes: A Systematic Review and Meta-analysis (Karanika S et al, CID 15 July 2016). The results of this study suggest that you shouldn't be an athlete (6% MRSA colonization rate), especially a wrestler (22% MRSA colonization rate). Additionally, the authors reported that colonization increases the risk of subsequent skin and soft tissue infection 7 times. If only it were safer to lay around on the beach this summer.

4) Addressing Infection Prevention and Control in the First U.S. Community Hospital to Care for Patients With Ebola Virus Disease: Context for National Recommendations and Future Strategies (Cummings KJ et al. Annals 5 July 2016). Authors from the CDC, Texas Health Presbyterian Hospital in Dallas and other other institutions describe the massive infection prevention response that followed the infection of two MICU nurses who cared for the index patient from Liberia. The responses included protocols for specimen handling, managing medical waste and standardized PPE with education and monitoring. Nothing particularly novel in 2016, but the article certainly highlights the massive efforts and costs associated with the N=1 response that was required because of a chronically underfunded public health and infection prevention infrastructure.

5) A Novel Microbiome Therapeutic Increases Gut Microbial Diversity and Prevents Recurrent Clostridium difficile Infection (Khanna S et al. J Infect Dis 15 July 2016). The authors describe an alternative method to fecal transplants that could potentially avoid donor screening among other barriers. They tested SER-109, which is encapsulated spores captured from healthy human donor stool that was treated with ethanol to eliminate pathogens, for the prevention of recurrent CDI. The cohort of patients had to have had >3 CDI cases in the prior 12 months and a clinical response to antibiotic therapy for their current CDI episode immediately prior to dosing of SER-109. The 15 patients in cohort 1 received high-dose capsules (15 on day 0 and 15 on day 1) and 15 patients in cohort 2 received lower dose capsules on a single day. Overall, 87% achieved the endpoint of no CDI at 8 weeks. If you're interested in reading more, there is an excellent accompanying editorial.

Antimicrobial Stewardship and C. difficile Therapy: It's Complicated

The CDC's Get Smart About Antibiotics Week (November 16-22, 2015) is upon us. To do our part, we bloggers are using this (and hopefully other) posts to "Highlight Get Smart Week on your website" as CDC suggested as an Activity Idea. Of course, the problem with getting smart about antibiotics is that it's really complicated. Sure, reducing unnecessary antibiotic use (e.g. don't treat viruses) seems simple, but the toolkits necessary to assist primary care physicians aren't yet fully developed (e.g. improved rapid diagnostics). And don't even think about inpatient stewardship. I've yet to see antibiotic selection guided by the existence of bacterial multidrug efflux pumps, for example, but hopefully that's coming too. This is not meant to be discouraging, it's just to say that we have a long road ahead and we must keep pushing forward with stewardship-focused basic science studies and clinical trials including implementation science.

With all that in mind, I came across what appears to be an important paper in the November 15 issue of JID by Brittany Lewis and colleagues at Memorial Sloan-Kettering. The authors asked a fairly simple question - what happens to gut flora when it's treated with C. difficile specific therapies and how does antibiotic selection alter colonization resistance to C. difficile, VRE, CRE and E. coli challenges. The authors designed their study around a typical antimicrobial stewardship question: should we treat C. difficile infection (CDI) with metronidazole, vancomycin or both?

Using a mouse model (9 mice per treatment-time point), each was treated for 3 days with metronidazole, vancomycin or both. Fecal samples were then tested for bacterial population diversity (16s sequencing) and susceptibility to C. difficile spore inoculation at 1, 3, 7, 14 and 21 days. As you can see in the figure below, most metronidazole-treated mice could not support C. difficile growth (red circles) after seven days, while many who received vanco or vanco+metro remained susceptible to infection out to 3 weeks. At 7 days and 14 days, 11% and 0% of metronidazole-treated mice were susceptible, respectively. In those treated with vanco, 89% were susceptible at day 3 and 100% were susceptible at day 7. This suggests that vancomycin might increase risk for recurrent infection compared to metronidazole.

Given those findings, it is not surprising that mice treated with metronidazole alone maintained a relatively stable microbiota (See figure below - click to enlarge), which could explain their reduced susceptibility to C. difficile. Among those treated with vanco or vanco+metro, mice with higher levels of disrupted microbial communities were less able to suppress C. difficile growth.

Perhaps more importantly in our fight against antibacterial resistance, a second aim of their study (see figure below) found that mice treated with vancomycin (pink circles) were far more susceptible to VRE, carbapenem-resistant K. pneumoniae and E. coli than metronidazole treated (black circles) or untreated mice (open circles) for at least two weeks post therapy.

In summary, in this sophisticated mouse model, exposure to oral vancomycin was associated with higher risk of C. difficile, a prolonged highly disrupted microbiota and an elevated risk of VRE, CRKP and E. coli colonization compared to those treated with metronidazole alone. There seems to be an increased push to treat CDI patients with oral vancomycin, but given these findings, one wonders if increased utilization of PO vancomycin might be right for an individual patient (although there might be higher recurrence), but wrong for society with increased emergence of VRE, CRKP and other pathogens. After reviewing this study, I'm surely a bit smarter about antibiotics, but unsure of how to treat patients with CDI...and so it goes.