mBio: MRSA – Making A House A Biome

MRSA - Photo Credit CDC

 

# 9804

 

From the Open Access journal mBio this morning, a report that suggests that MRSA can hang around a household, bounce repeatedly between family members, and evolve into a unique `family’ strain, over a period of several years.

Previously we’ve looked at MRSA colonization, where the CDC quantified colonization by stating:

 

While 25% to 30% of people are colonized* in the nose with staph, less than 2% are colonized with MRSA (Gorwitz RJ et al. Journal of Infectious Diseases. 2008:197:1226-34.).

*Colonized:
When a person carries the organism/bacteria but shows no clinical signs or symptoms of infection. For Staph aureus the most common body site colonized is the nose.

 

However, in  Firefighters & Paramedics At Greater Risk Of MRSA and Firefighters & MRSA Revisited we looked at research showing a 10x’s greater incidence of MRSA colonization (20%) among a sampling of firefighters tested in Washington State.

 

As we learn from an American Society of Microbiology press release today (see MRSA can linger in homes, spreading among its inhabitants), a 2012 study found up to 50% of family contacts in households with one SSTI (Skin or soft Tissue Infection) with MRSA were colonized with the resistant bacteria.

They describe the findings of today’s study as:

 

Households can serve as a reservoir for transmitting methicillin-resistant Staphylococcus aureus (MRSA), according to a study published this week in mBio®, the online open-access journal of the American Society for Microbiology. Once the bacteria enters a home, it can linger for years, spreading from person to person and evolving genetically to become unique to that household.

<SNIP>

he researchers found that isolates within households clustered into closely related groups, suggesting a single common USA300 ancestral strain was introduced to and transmitted within each household. Researchers also determined from a technique called Bayesian evolutionary reconstruction that USA300 MRSA persisted within households from 2.3 to 8.3 years before their samples were collected, and that in the course of a year, USA300 strains had a 1 in a million chance of having a random genetic change, estimating the speed of evolution in these strains. Researchers also found evidence that USA300 clones, when persisting in households, continued to acquire extraneous DNA.

"We found that USA300 MRSA strains within households were more similar to each other than those from different households," said senior study author Michael Z. David, MD, PhD, an assistant professor of edicine at the University of Chicago. Although MRSA is introduced into households rarely, he said, once it gets in, "it can hang out there for years, ping-ponging around from person to person. Our findings strongly suggest that unique USA300 MRSA isolates are transmitted within households that contain an individual with a skin infection."

(Continue . . .)

A link, and the abstract to the entire mBio report can be accessed below:

 

 

 

Transmission and Microevolution of USA300 MRSA in U.S. Households: Evidence from Whole-Genome Sequencing

Md Tauqeer Alam^a, Timothy D. Read^a,b, Robert A. Petit III^a, Susan Boyle-Vavra^c, Loren G. Miller^d, Samantha J. Eells^d, Robert S. Daum^c, Michael Z. David^c,e

ABSTRACT

Methicillin-resistant Staphylococcus aureus (MRSA) USA300 is a successful S. aureus clone in the United States and a common cause of skin and soft tissue infections (SSTIs). We performed whole-genome sequencing (WGS) of 146 USA300 MRSA isolates from SSTIs and colonization cultures obtained from an investigation conducted from 2008 to 2010 in Chicago and Los Angeles households that included an index case with an S. aureus SSTI.

Identifying unique single nucleotide polymorphisms (SNPs) and analyzing whole-genome phylogeny, we characterized isolates to understand transmission dynamics, genetic relatedness, and microevolution of USA300 MRSA within the households. We also compared the 146 USA300 MRSA isolates from our study with the previously published genome sequences of the USA300 MRSA isolates from San Diego (n = 35) and New York City (n = 277). We found little genetic variation within the USA300 MRSA household isolates from Los Angeles (mean number of SNPs ± standard deviation, 17.6 ± 35; π nucleotide diversity, 3.1 × 10⁻⁵) or from Chicago (mean number of SNPs ± standard deviation, 12 ± 19; π nucleotide diversity, 3.1 × 10⁻⁵).

The isolates within a household clustered into closely related monophyletic groups, suggesting the introduction into and transmission within each household of a single common USA300 ancestral strain. From a Bayesian evolutionary reconstruction, we inferred that USA300 persisted within households for 2.33 to 8.35 years prior to sampling. We also noted that fluoroquinolone-resistant USA300 clones emerged around 1995 and were more widespread in Los Angeles and New York City than in Chicago. Our findings strongly suggest that unique USA300 MRSA isolates are transmitted within households that contain an individual with an SSTI. Decolonization of household members may be a critical component of prevention programs to control USA300 MRSA spread in the United States.

IMPORTANCE USA300, a virulent and easily transmissible strain of methicillin-resistant Staphylococcus aureus (MRSA), is the predominant community-associated MRSA clone in the United States. It most commonly causes skin infections but also causes necrotizing pneumonia and endocarditis. Strategies to limit the spread of MRSA in the community can only be effective if we understand the most common sources of transmission and the microevolutionary processes that provide a fitness advantage to MRSA.

We performed a whole-genome sequence comparison of 146 USA300 MRSA isolates from Chicago and Los Angeles. We show that households represent a frequent site of transmission and a long-term reservoir of USA300 strains; individuals within households transmit the same USA300 strain among themselves. Our study also reveals that a large proportion of the USA300 isolates sequenced are resistant to fluoroquinolone antibiotics. The significance of this study is that if households serve as long-term reservoirs of USA300, household MRSA eradication programs may result in a uniquely effective control method.

(Continue . . . )

 

Study: Weighing The Risks Of MRSA Colonization

MRSA - Photo Credit CDC

# 6807

 

The CDC tells us, in their Definition of MRSA page, that:

 

While 25% to 30% of people are colonized* in the nose with staph, less than 2% are colonized with MRSA (Gorwitz RJ et al. Journal of Infectious Diseases. 2008:197:1226-34.).

*Colonized:
When a person carries the organism/bacteria but shows no clinical signs or symptoms of infection. For Staph aureus the most common body site colonized is the nose.

 

 

Although 2% doesn’t sound like a lot, there are signs that number may be increasing. Once considered primarily a hospital acquired infection, CA-MRSA (community acquired) is growing in incidence.

 

As an example, in Firefighters & Paramedics At Greater Risk Of MRSA and Firefighters & MRSA Revisited we looked at research showing a 10x’s greater incidence of MRSA colonization (20%) among a sampling of firefighters tested in Washington State.

 

Since one person’s colonization can become another person’s infection, topics of debate have included:

 

1. What risks are there to the individual from long-term colonization?
2. What risks are there to others In the Community or a household?
3. What risks are there to others in a hospital or long-term care environment?
4. What (if any) steps should be taken to decolonize carriers, and in what setting (hospital admission? Outpatient?) is decolonization desirable and effective?

 

There are, it seems, few easy answers. 

 

Mary McKenna, editor of the terrific Superbug Blog, took a look at the problems inherent with the decolonization of MRSA carriers in 2009 with:

 

Decolonization: disappointing news 

The upshot was that while studies have shown that decolonization procedures on hospitalized patients about to undergo surgery can reduce infections, the value to other patients is far less clear.

 

And as Maryn points out, overuse of mupirocin – the primary antibiotic used to decolonize patients –can lead to increased resistance over time.

 

And Mary also tells of a paper published in Infection Control and Hospital Epidemiology, that evaluated the success of decolonization protocols in 3 major Illinois hospitals, that less than reassuring results: a temporary reduction in patients’ being colonized with MRSA, but no success in preventing infection.

 

In 2011, the Infectious Diseases Society of America published their clinical practice guidelines for treating MRSA in adults and children, where they endorse `decolonization’, but only under select scenarios (note SSTI = Skin & Soft Tissue Infection):

 

14. Decolonization may be considered in selected cases if:

• i. A patient develops a recurrent SSTI despite optimizing wound care and hygiene measures (C-III).

• ii. Ongoing transmission is occurring among household members or other close contacts despite optimizing wound care and hygiene measures (C-III).

 

• ii. Contacts should be evaluated for evidence of S. aureus infection:
• a. Symptomatic contacts should be evaluated and treated (A-III); nasal and topical body decolonization strategies may be considered following treatment of active infection (C-III).
• b. Nasal and topical body decolonization of asymptomatic household contacts may be considered (C-III)

 

But what, if anything, to do about asymptomatic carriers who are colonized, but not infected with MRSA remains up in the air.

 

Hospital strategies to contain and control MRSA range from passive surveillance to aggressive `search & destroy’ policies – with variations in between.

 

Passive surveillance – which is the most commonly used protocol in the United States – involves  testing only those who have clinical signs or symptoms of
MRSA.

Since patients may be colonized without exhibiting outward signs, this will fail to detect a great many carriers of the bacteria.

Active Surveillance – requires the testing of high risk admissions (ie.  Hx of MRSA, Antibiotic Use, Admission to Hospital in past year, Resident of Long-term care facility, etc.) for the bacteria.

Patients testing positive may be isolated and decolonized or treated, with strict infection control precautions enforced.

Universal Surveillance – takes the above steps to a higher level, where all admissions and personnel are routinely swabbed and tested for MRSA.

“Search & Destroy” – which is the most intensive protocol, has been used successfully in countries like Finland, Denmark and the Netherlands.

It combines Active or Universal Surveillance with testing of patients in high-risk wards at intervals and prior to discharge.

 

The reluctance to adopt the more aggressive of these measures have been the costs, the inconvenience to patients and their visitors, and quite frankly, objections by some hospital staff over being repeatedly tested.

A recent study appearing in Critical Care Medicine, looked at the effects of a strict S&D policy instituted at a rural trauma center, and found an immediate reduction specific types of HAIs (Hospital Acquired Infections) after implementation.

 

Search & Destroy (S&D): Eradication of Mrsa Colonization Is Associated With Decreased Mrsa Infections in Trauma Patients

Borst, Gregory; Waibel, Brett; Toschlog, Eric; Coogan, Michael; Skarupa, David; Rotondo, Michael; Ramsey, Keith

Conclusions: Search and destroy is associated with significant decreases in the incidence of MRSA VAP and CLABSI in trauma patients. Decreases in MRSA CAUTI and wound infections were also seen after the implementation of this program. Pre-emptive strategies to identify and eradicate MRSA are worthwhile endeavors in terms of preventing nosocomial infection.

 

Despite its critics, S&D policies have often shown reductions in HAIs. 

 

Which brings us to another study, published last week in the journal Antimicrobial Agents and Chemotherapy, that finds (among a relatively small cohort of patients) that colonization with MRSA posed a substantial risk of MRSA infection, increased mortality, or readmission to the hospital, compared to patients without MRSA colonization.

 

 

Long-Term Risk for Readmission, Methicillin-resistant Staphylococcus aureus (MRSA) Infection, and Death among MRSA-Colonized Veterans.

Quezada Joaquin NM, Diekema DJ, Perencevich EN, Bailey G, Winokur PL, Schweizer ML.

Source

Division of Infectious Diseases.

Abstract

Background: While numerous studies assessed outcomes of MRSA colonization over the short term, little is known about longer-term outcomes after discharge. An assessment of long-term outcomes could inform the utility of various MRSA prevention approaches.

Methods: A matched cohort study was performed among Veterans Affairs (VA) patients screened for MRSA colonization between the years 2007 and 2009 and followed to evaluate outcomes until 2010. Cox proportional hazard models were used to evaluate the association between MRSA colonization and long-term outcomes such as infection-related readmission, and crude mortality.

Results: 404 veterans were included, 206 of whom were MRSA carriers and 198 who were non-carriers. There were no culture-proven MRSA infections on readmission among the non-carriers, but 13% of MRSA-carriers were readmitted with culture proven MRSA infections on readmission (P<0.01).

MRSA carriers were significantly more likely to be readmitted, be readmitted more than once due to proven or probable MRSA infections, and be readmitted within 90 days of discharge compared to non-carriers (p<0.05). Infection-related readmission (adjusted hazard ratio [AHR] =4.07; 95% confidence interval [CI]: 2.16, 7.67) and mortality (AHR=2.71; 95% CI: 1.87, 3.91) were significantly higher among MRSA carriers compared to non-carriers, after statistically adjusting for potential confounders.

Conclusions: Among a cohort of VA patients, MRSA carriers are at high risk of infection-related readmission, MRSA infection and mortality compared to non-carriers. Non- carriers are at very low risk of subsequent MRSA infection. Future studies should address whether interventions such as nasal or skin decolonization could result in improved outcomes for MRSA carriers.

Although based on a small cohort, this study suggests that being colonized (but not infected) with MRSA is a significant risk factor for future infection, and if these findings can be confirmed by others, may influence how MRSA colonization is viewed in the future.

 

Despite some recent improvements in MRSA rates among hospitalized patients in the United States, HAIs (which include many other pathogens) continue to exact a heavy toll. This oft quoted assessment from the CDC on the burden of Hospital Acquired Infections in the United States is from 2010.

 

A new report from CDC updates previous estimates of healthcare-associated infections. In American hospitals alone, healthcare-associated infections account for an estimated 1.7 million infections and 99,000 associated deaths each year. Of these infections:

• 32 percent of all healthcare-associated infection are urinary tract infections
• 22 percent are surgical site infections
• 15 percent are pneumonia (lung infections)
• 14 percent are bloodstream infection

For more on MRSA, and many other antibiotic-resistant threats, you can do no better than to visit Maryn McKenna’s terrific Superbug Blog, and to read her book Superbug: The Fatal Menace of MRSA . . . which won last year’s  NASW Science in Society Journalism Award.

You’ll find my review of her book HERE

Coffee, Tea, or MRSA?

 

 

# 5691

 

 

An interesting study appears in the Annals of Family Medicine that looks at the rate of nasal carriage of MRSA (methicillin-resistant Staphylococcus aureus) among hot coffee & tea drinkers compared to those who abstain.

 

As we’ve discussed before, a small percentage of the population is known to carry either MRSA or non-resistant S. aureus in their nasal cavities.

 

This from the CDC:

 

Definition of MRSA

While 25% to 30% of people are colonized* in the nose with staph, less than 2% are colonized with MRSA (Gorwitz RJ et al. Journal of Infectious Diseases. 2008:197:1226-34.).

*Colonized:
When a person carries the organism/bacteria but shows no clinical signs or symptoms of infection. For Staph aureus the most common body site colonized is the nose.

 

In Firefighters & Paramedics At Greater Risk Of MRSA from last year, and a follow up called Firefighters & MRSA Revisited from last month we looked at research showing a 10x’s greater incidence of MRSA colonization (20%) among a sampling of firefighters tested in Washington State.

 

Which brings us to today’s study that analyzed data from the 2003–2004 National Health and Nutrition Examination Survey and found that non-institutionalized people who consumed either hot tea or coffee were roughly half as likely to carry MRSA compared to those who didn’t.

 

While interesting, exactly what to make of their findings isn’t clear.

 

Although the authors attempted to account for other external variables (age, income, self-reporting bias) there could be other factors at work here besides just the consumption of these hot beverages.

 

The old adage, "Correlation does not imply causation"  applies.

 

Just because two phenomena tend to happen in close proximity to one another does not necessarily mean that one causes the other.

 

Still . . . the results are intriguing.

 

 

Tea and Coffee Consumption and MRSA Nasal Carriage

Eric M. Matheson, MD, MS, Arch G. Mainous III, PhD, Charles J. Everett, PhD and Dana E. King, MD, MS

Department of Family Medicine, Medical University of South Carolina, Charleston, South Carolina

CONCLUSIONS Consumption of hot tea or coffee is associated with a lower likelihood of MRSA nasal carriage. Our findings raise the possibility of a promising new method to decrease MRSA nasal carriage that is safe, inexpensive, and easily accessible.

 

 

You can read the entire study here, including their methodology which relied on a small subset (n=5555) of the population – deemed to be representative of the greater non-institutionalized population of the United States.

 

The authors conclude by stating:

 

Our findings of reduced odds of MRSA nasal carriage among tea and coffee drinkers raise the possibility of a promising new alternative to antibiotics that is safe, inexpensive, and easily accessible.

 

Perhaps.

But I’m left with one nagging thought.

 

In the two studies I cited on firefighters at the top of the blog, nasal carriage was found to be 10 times higher than the general population.

 

Unless things have changed greatly since I was a paramedic (which admittedly was long ago and in a galaxy far, far away . . . ) – firefighters and paramedics are prodigious consumers of hot coffee.

 

Which – if this latest study is aiming us in the right direction - makes you wonder what their rate of nasal carriage would have been without their daily consumption of copious cups of coffee.

 

I sense another study is needed.