Staphylococcus aureus (S. aureus) is a widely distributed bacterial pathogen. The CDC reported that in 2004 about 30% of the U.S. population was found to have S. aureus colonizing their nasal passages.1 Historically, S. aureus infections occurred more commonly among individuals with immune deficiencies, or those in hospital settings. However, an urgent concern is the recent increase of S. aureus infections among young and otherwise healthy individuals in the community. Certain strains of these bacteria are developing increasing resistance to many commonly used antibiotics, such as methicillin. These strains are called methicillin-resistant S. aureus (MRSA). MRSA has been referred to as a “superbug” due to the serious clinical consequences of infections and the inability of many current antibiotics to effectively treat patients. There were an estimated four million Americans colonized by MRSA strains in 2004 (1.5% of the population), nearly double the rate from the last survey in 2001.1 S. aureus is a common cause of skin infections, as well as infections that are more widely disseminated throughout the body, called invasive infections. The high incidence of these infections places a huge burden on the U.S. health care system.
Staphylococcus aureus Skin Infections
S. aureus is the leading cause of skin and soft tissue infections (SSTI), also referred to as skin and skin structure infections. Methicillin-resistant S. aureus (MRSA) is a predominant cause of hospital- and community-acquired SSTI. SSTIs are a particular concern in the armed forces. A recent S. aureus epidemiological study involving 56 million person-years from 2005-2010 was conducted among beneficiaries of the military’s Tricare health system. The annual rate of S. aureus SSTIs (54% MRSA) among non-active duty beneficiaries was about 85/100,000, which would correspond to roughly 300,000 cases in the US population annually. Active duty beneficiaries were at a five-fold higher risk for S. aureus SSTIs (63% MRSA).2 Patients with S. aureus SSTIs have a 50% risk of having a recurrent infection within six months.3 Household contacts of patients with MRSA SSTIs have been reported to have infection rates of 15% within a year.4 Other risk groups include individuals living in close quarters or having close physical contact. The CDC cites those living in dormitories, military barracks, and correctional facilities as being at increased risk for MRSA SSTIs. Other risk groups are children and workers in day care centers and athletes in high-contact sports.5
Staphylococcus aureus Invasive Infections
In 2011, there were an estimated 80,000 cases of invasive MRSA in the U.S., which led to 11,000 deaths (14% mortality rate).6 This means that despite the currently available antibiotics, about one in seven patients with invasive MRSA will die. This highlights the need for a safe and effective vaccine against S. aureus and MRSA to prevent these life-threatening infections. Results from two Phase 1 clinical trials in 200 healthy adults demonstrated that the NDV-3 vaccine was safe, well-tolerated and induced strong antibody and T-cell immune responses to the vaccine in healthy adults.
Most invasive MRSA cases (79%) in the U.S. were determined to have had their onset in hospitalized patients or in patients who have had recent contact with the health care system. Certain medical procedures in hospitalized or institutionalized patients lead to increased rates of MRSA infections, including surgery or the use of invasive devices like central venous catheters and ventilators. Patients who have previously received long courses of antibiotic therapy are also at particularly high risk for MRSA infections. During 2011, 15,000 U.S. patients undergoing kidney dialysis (3.6%) contracted invasive MRSA infections.6
- Gorwitz, RJ, Kruszon-Moran, D., McAllister, S. K., McQuillan, G., McDougal, L. K., Fosheim, G. E., Jensen, B. J., Killgore, G., Tenover, F. C., Kuehnert, M. J. Changes in the prevalence of nasal colonization with Staphylococcus aureus in the United States, 2001-2004. J. Infect. Dis. 2008; 197: 1226-34
- Landrum ML, Neumann, C., Cook, C., Chukwuma, U., Ellis, M. W., Hospenthal, D. R., Murray, C. K. Epidemiology of Staphylococcus aureus blood and skin and soft tissue infections in the US military health system, 2005-2010. JAMA 2012; 308(1): 50-59.
- Fritz SA, Camins, B. C., Eisenstein, K. A., Fritz, J. M., Epplin, E. K., Burnham, C. A., Dukes, J., Storch, G. A. Effectiveness of measures to eradicate Staphylococcus aureus carriage in patients with community-associated skin and soft-tissue infections: a randomized trial. Infect. Control Hosp. Epidemiol. 2011; 32(9): 872-880.
- Fritz SA, Hogan, P. G., Hayek, G., Eisenstein, K. A., Rodriguez, M., Epplin, E. K., Garbutt, J., Fraser, V. J. Household versus individual approaches to eradication of community-associated Staphylococcus aureus in children: a randomized trial. Clin. Infect. Dis. 2012; 54(6): 743-751.
- US CDC MRSA People at Risk, http://www.cdc.gov/mrsa/riskfactors/index.html.
- U.S. Centers for Disease Control, Active Bacterial Core Surveillance Report, MRSA, 2011 (http://www.cdc.gov/abcs/reports-findings/survreports/mrsa11.pdf).