For whom the bug tolls: MRSA kills more people in U.S. annually than HIV/AIDS

Experts say 18,650 annual deaths is an underestimate

The recent widely publicized finding that methicillin-resistant Staphylococcus aureus now kills more people annually than HIV/AIDS in the United States could result in a shift in public health priorities and funding as the true impact of MRSA in health care and the community comes to painful light.

Moreover, the findings by researchers at the Centers for Disease Control and Prevention inevitably will lead to increasing demands by angry consumers and impatient lawmakers that health care facilities be subjected to more oversight to ensure they are taking measures to eradicate a bug that has become a national nemesis. For example, increased frequency of health department inspections of hospitals is among the topics under discussion in light of the findings.

"We thought by calculating for one year the number of invasive infections — we couldn't count them all so we focused on the most severe and the number of deaths — then we would be able to compare [MRSA] with other public health priorities," says R. Monina Klevens, DDS, MPH, lead author of the study and an epidemiologist in the CDC division of health care quality promotion. "[Now we can] say, 'What are we going to do about this?'"

The CDC researchers analyzed population-based surveillance data for invasive MRSA infections at nine sites participating in the Active Bacterial Core system to estimate the rate of invasive MRSA infections in 2005. The rate was a staggering 31.8 per 100,000 people, but the death toll estimates were the real kicker. "Based on 8,987 observed cases of MRSA and 1,598 in-hospital deaths among patients with MRSA, we estimate that 94,360 invasive MRSA infections occurred in the United States in 2005; these infections were associated with death in 18,650 cases," the authors concluded.1

An accompanying editorial by Elizabeth A. Bancroft, MD, a medical epidemiologist at the Los Angeles County health department, drew the compelling comparison with HIV, noting that "if their projection is accurate, these deaths would exceed the total number of deaths attributable to human immunodeficiency virus/AIDS in the United States in 2005."2

MRSA hits the big time

The mortality projections reflect in part the rampant rise of one pathogen while another is beaten back from a uniformly fatal to a chronic disease by better drugs and treatments. For the record, the CDC estimated that 17,011 people died of AIDS in 2005, and the disease, of course, remains a global scourge in areas without access to effective drugs and treatment options.3 Still, reporting that MRSA bacteria had eclipsed the annual death toll of a virus that has acquired the infectious disease infamy of plague and the 1918 pandemic flu resonated in headlines, sound bites, and even Congressional hearings. In short, MRSA has hit the big time, and ICPs can only hope that additional funding and resources will be coming their way to help reduce its deadly toll.

"Just thinking about the relative resources that we have to combat and prevent [MRSA], maybe this [comparison] will help with this organism, shed some light, and get some resources," Bancroft tells Hospital Infection Control. Moreover, she drove the point home in the editorial by noting that the findings likely represent an underestimate and "the total burden of MRSA may be much greater than what was estimated in this study."

Concurring was the lead researcher of a different but equally troubling study, the MRSA prevalence study unveiled at this year's meeting of the Association for Professionals in Infection Control and Epidemiology. William Jarvis, MD, a former leading CDC hospital outbreak investigator now in private consulting, found that 46 out of every 1,000 patients in participating health care facilities of all types and sizes were colonized or infected with MRSA. As dramatic as Klevens' and colleagues' findings were — more than 18,000 fatal infections a year — the study underestimated the death toll of MRSA, he says.

"It is a minimum estimate of mortality because they only looked at invasive disease," he tells HIC. "If you looked at what they defined as invasive and what they actually captured, over 75% of it was bloodstream infections. It's basically a blood culture study. [But] you have MRSA surgical site infections and vent-associated pneumonias that lead to deaths. There are other MRSA infections that lead to death that were not captured in that study."

Regarding the old argument about whether MRSA was arising independently in the community or "escaping" from the hospital, the answer in the Klevens study tilted toward the latter. "The majority of invasive MRSA cases occurred outside of the hospital (58%) but among persons with established risk factors for MRSA, such as a history of hospitalization in the past year," the CDC researchers concluded. "Patients with health care risk factors and community-onset disease likely acquired the pathogen from their health care contacts, such as those from a recent hospitalization or nursing home residence. Molecular analysis suggests that most of these infections were caused by MRSA strains of health care origin."

Prevention focused on health care

If the infections represent acquisition during acute care, it follows that strategies to prevent MRSA should be focused on health care settings, the authors reasoned. "Because most of the infections that we found were health care-associated — and we know what prevention strategies work in the health care setting — that should be our priority," Klevens says. The corollary to that logic is that preventing MRSA transmission in the community is difficult and effective strategies are still under refinement. While health care remains the prime risk factor, it bears emphasis that the study found nearly 14% of invasive MRSA infections were truly community-acquired. Those numbers could increase as the predominant USA300 strain continues to spread throughout the country.

Overall, the MRSA study found that 2,389 (26.6%) infections were hospital-onset; 1,234 (13.7%) were community-associated; and 114 (1.3%) could not be classified. Again, the majority (58%) of MRSA cases were among patients who had health care risk factors but community onset of disease. Most of them were infected with the USA100 genotype, a traditional health care strain of MRSA. Though various and sundry caveats were included regarding the accuracy of the various percentages, the upshot is that the increasing pressure to prevent MRSA will fall to the health care system. Strategies to prevent MRSA infections in hospitals, including hand washing and environmental cleaning, are well known but "imperfectly practiced," Bancroft understated in her editorial. She called for more public health oversight of infection control in health care, noting that "in California, restaurants are routinely inspected more frequently (once per year) than nursing homes (once every two years), hospitals (once every three years), or physicians' offices (never). To be serious about controlling nosocomial disease and antibiotic resistance will require cleaning up the source."

Health care inspections — which could carry the threat of licensure loss — could focus on infection prevention process measures rather than rate numbers, she says, noting that it is done "in the same way that public health currently goes into restaurants to make sure that people are adhering to requirements for safe food handling."

In addition, a growing number of states are passing MRSA laws requiring infection reporting and/or active surveillance cultures (ASC) to detect colonized patients. "I think we need government to take a lead," Jarvis says. "One of the major reasons why we already have seven states that have MRSA legislation — and we'll have more this year — is because the public is tired of waiting for hospitals to do the right thing. There are many that argue that we can't do anything about this. Well, we have 200 studies showing that the approach of risk assessment, active surveillance testing, contact isolation, hand hygiene, and environmental cleaning works. We need to get our hospitals to start implementing that and then we will see a positive impact, regardless of what happens in the community."

The CDC has been less enthusiastic about active surveillance, with its most recent guidelines calling for hospitals to go to more aggressive measures such as ASC if rates of resistant pathogens including MRSA are not going down.4 "It's very important to show [in the study] that nearly 20,000 people die each year of MRSA," Jarvis says. "CDC has recommended that the entire population be screened for HIV when less than 20,000 die, but has not recommended that hospital populations be screened when this large number of patients die [from MRSA]." However, the CDC and infection control professionals also have emphasized that MRSA is not the only bug in town. There are some disturbing trends, for example, among gram-negative pathogens that shouldn't be swept aside by the national focus on MRSA.

National reporting likely on the way

That said, it will be hard to get MRSA to budge much on the national radar after recent reports that included fatal community infections in schoolchildren. Yet many are surprised to find — despite all its recent infamy — that MRSA has not traditionally been considered of sufficient public health significance to warrant reporting to state health departments. That is subject to change. Bancroft said the aforementioned rate of invasive MRSA found by Klevens and colleagues was "astounding." It means the rate of invasive MRSA is greater than the combined rate in 2005 for invasive pneumococcal disease (14.1 per 100,000), invasive group A. streptococcus (3.6 per 100,000), invasive meningococcal disease (0.35 per 100,000), and invasive H. influenzae (1.4 per 100,000), she reported.

"I was surprised by it because this is not a disease usually followed by departments of public health," she says. "I was surprised at the rate — especially in relation to all of these other diseases that we do consider of enough public health importance to follow up on. I think there were very few of us that realized how large the rate was going to be in comparison to other diseases that we commonly follow and consider to be significant pathogens."

In addition, few antibiotic-resistant infections overall are on the list of reportable diseases in the United States, with the three currently listed being drug-resistant Streptococcus pneumoniae, vancomycin-intermediate S. aureus, and vancomycin-resistant S. aureus.

"In several states, [MRSA] is on the list of reportable infections or certainly the legislators are thinking about it," she says. "I think we will see increased reporting of this organism. On the other hand, it is tough to do reporting for [MRSA] for both health care facilities and for public health. There are so many cases of MRSA that the resources it takes to follow up on all of them are limited for both public health and hospitals." Electronic reporting from laboratory systems could be a major part of the answer. "That means going straight from the lab information systems to public health, but if it still has to be done manually, it will be tough."

References

  1. Klevens RM, Morrian MA, Nadle J. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA 2007; 298:1,763-1,771.
  2. Bancroft EA. Editorial: Antimicrobial resistance — It's not just for hospitals. JAMA 2007; 298:1,803-1,804.
  3. Centers for Disease Control and Prevention. HIV/AIDS Surveillance Report, 2005. Vol. 17. Revised ed. Atlanta: U.S. Department of Health and Human Services; 2007.
  4. Centers for Disease Control and Prevention. Siegal JD, Rhinehart E, Jackson L, et al. The Healthcare Infection Control Practices Advisory Committee Management of Multidrug-Resistant Organisms in Healthcare Settings, 2006. On the web at: www.cdc.gov.