Infectious Disease - Staphylococcus Aureus

Infectious disease - Staphylococcus aureus

Review of the Epidemiology of Staphylococcus aureus

As the percentage of elderly in the United States continues to increase, it is reasonable to expect more and more people to become hospitalized for one reason or another in the coming years. One of the more challenging problems associated with hospitals stays to date has been nosocomial infections which are caused primarily by Staphylococcus aureus. Furthermore, the pathogen appears to be developing specific resistances to the pharmacological weapons developed to date, and S. aureus continues to represent a threat for many elderly people and those who are already weakened by other physical problems. To determine the cause and potential continuing threat represented by this bacterium, this paper provides a review of the epidemiology of Staphylococcus aureus to determine the development of the current body of knowledge about the disease, followed by a summary of the research and salient findings in the conclusion.

Review and Discussion

Background and Overview.

While the world has never been a sterile place, it would seem that one of the most prevalent and virulent of mankind's microscopic foes has always been Staphylococcus aureus. In fact, staphylococci are ubiquitous, and approximately 30% to 50% of healthy human beings will be carrying staphylococci at any one time (Eidson, Olson & Sewell, 1997). Staphylococcus aureus is a genus of spherical bacteria of the family Micrococcaceae; the Staphylococcus aureus is universally present in enormous numbers on the mucous membranes and skin of humans and other warm-blooded animals. The umbrella term, "staphylococcus" is popularly used for all the species of the family, and is a reference to the cells' tendency to aggregate in grapelike clusters (Staphylococcus, 2005). Staphylococci are microbiologically characterized as gram-positive (in young cultures), non-spore-forming, nonmotile, facultative anaerobes (e.g., not requiring oxygen); the cells of S. aureus average 1 mm (micrometer; 1 mm = 10-6 meter) in diameter and are usually clustered (Staphylococcus, 2005).

The two variants of the species S. aureus that represent the biggest threat to humanity are responsible for wound infections, boils, and other human skin infections as well as one of the most common causes of food poisoning; in addition, S. aureus is also responsible for causing udder inflammation in domestic animals and breast infections in women. The experts advise that'd. aureus is a challenging pathogen in hospital settings because of its resistance to antibiotics; by contrast, S. epidermis is a milder pathogen that is opportunistic in people who already have lowered resistance (Staphylococcus, 2005).

Etiology and Treatment of Staphylococcus aureus.

In their essay, "Microbial Menace," Chikami and Murphy (1998) report that the development and introduction of antibiotic resistance and the interaction among the disease-causing organisms has been well illustrated by the evolution of antibiotic resistance in Staphylococcus aureus, which is one of the leading causes of hospital-acquired infections such as pneumonia or skin infections. "In the pre-antibiotic era," they say, "staph infections were an important cause of sickness and death. The pathogen was initially susceptible to treatment with penicillin, although resistance to the drug began to develop shortly after penicillin's introduction in the 1940s" (p. 12). Penicillin was highly effective at first with S. aureus, and was used extensively for this purpose with burn victims; because it is an opportunistic pathogen, once the protective skin is damaged by fire, staphylococci can enter the body, where they circulate and multiply in the bloodstream, resulting in high fevers, shock, and even death (Levy, 1992). In this regard, "Penicillin was so uniquely active that small amounts of culture fluids could produce this killing effect," Levy (1992) says. "And, more importantly, it triumphed over a very common and deadly bacterium, Staphylococcus aureus, which caused skin infections, often leading to blood-borne dangerous septic disease" (p. 37). Over the years, though, S. aureus has acquired the ability to produce an enzyme (beta-lactamase) that was able to overcome the active ingredients in penicillin (Chikami & Murphy, 1998).

By the late 1950s, various strains of S. aureus had acquired resistance to penicillin and to virtually all other available systemic antibiotics, including erythromycin, streptomycin, and the tetracyclines; these strains of S. aureus were all associated with outbreaks of nosocomial infections; however, the introduction of semisynthetic penicillins (e.g., methicillin, which are not inactivated by beta-lactamase), and the cephalosporin antibiotics (e.g., cephalothin, cephaloridine, and cefazolin), during the 1960s represented a therapeutic advance in the treatment of infections caused by these antibiotic-resistant pathogens (Chikami & Murphy, 1998).

The organism adapted again, however, and methicillin-resistant strains of S. aureus (MRSA) began being identified as early as 1961; at the time, these organisms were associated with infections in Europe, but they have since become widespread around the world. According to these authors, "In the United States, the proportion of S. aureus isolates resistant to methicillin and reported to the National Nosocomial Infections Surveillance system increased from 2% in 1975 to 35% in 1996" (Chikami & Murphy, 1998, p. 13). Further, new strains of S. aureus have also become resistant to other antibiotics in the usual weapons in the pharmacology (Chikami & Murphy, 1998). In addition, during the late 1970s and early 1980s, there was an outbreak of Toxic Shock Syndrome (TSS) that was caused by S. aureus; the bacterium's toxins are amplified by several synthetic fibers that were being used in tampons at the time to increase absorbency. As a result of this outbreak, more than 50 women died and more than a thousand suffered (Perlingieri, 2004).

Today, clinicians have their choice of several powerful antibiotics to treat staph infections. One, developed in 1958, is known as "vancomycin"; this has been the drug of choice used to treat infections caused by resistant strains of S. aureus (Chikami & Murphy, 1998). Even vancomycin, though, has proven vulnerable to resistant organisms over time. According to these authors, "In fact, recent reports from Japan and the United States of strains of MRSA with reduced susceptibility to vancomycin have caused serious concern in the medical community" (Chikami & Murphy, 1998, p. 13). The emergence of these variant strains increases the possibility that fully resistant strains may develop in the future and that currently available antibiotics will be ineffective for treating infections caused by this pathogen (Chikami & Murphy, 1998). Other drugs of choice for treating MRSA, such as Zyvox, are prohibitively expensive for many patients (Caldwell, 2003).

Current and future trends. A future epidemic of MRSA is becoming increasingly possible because it is readily spread through skin-to-skin contact, with the condition typically manifesting itself in painful, deep abscesses; furthermore, since the outbreak of the usually nonfatal bacteria surfaced in Los Angeles in 2002, MRSA has been spread to virtually every major city in the country (Caldwell, 2003). While it may not kill someone outright (although it does increase the risk of mortality in the elderly and those who are have already weakened immune systems), MRSA is a persistent and challenging bacterium to treat, and the gay community in particular appears to be a higher risk for contracting it outside of hospital settings as well.