Historical Overview of MRSA

In order to better understand the history and development of methicillin-resistant Staphylococcus aureus (MRSA), we need to start from the development of the antibiotic drug penicillin, which is integral to this topic. Penicillin was introduced in 1941 and it was only one year later, in 1942, that penicillin-resistant strains of Staphylococcus aureus were first reported in hospitalized patients. Community strains of S. aureus remained sensitive to penicillin for several years. By the 1970s, penicillin resistance was widespread in the community as well as within healthcare facilities.

Methicillin, a semi-synthetic penicillin derivative, was introduced in 1960. MRSA had been identified within a short period of time after methicillin was first applied to the handling of Staphylococcus aureus and other types of infectious bacteria. The first nosocomial (hospital) outbreak in the United States occurred in 1968 in Boston, Massachusetts. MRSA made its first major public appearance in the United States in 1981 among intravenous drug users. Staphylococcus aureus is often called a "superbug" because of its power to adapt and become immune to many types of antibiotics. Staph infections, including MRSA, occur most frequently among persons who have weakened immune systems in hospitals and other healthcare facilities, such as nursing homes and kidney dialysis centers. These healthcare-associated staph infections can take the form of surgical wound infections, urinary tract infections, bloodstream infections (sepsis) and pneumonia. It is easy to learn and recognize most of the symptoms of MRSA, which are described in detail on the symptoms page.

MRSA Categorization by Source of Infection

In the scientific literature, MRSA infections are categorized into three groups by where the Staphylococcus aureus bacteria are acquired:

HA-MRSA refers to hospital or healthcare-acquired methicillin-resistant Staphylococcus aureus. Nosocomial infections are acquired in a hospital or other healthcare related institution or in individuals receiving healthcare, such as kidney dialysis, on an ongoing basis. According to the U.S. Centers for Disease Control and Prevention (CDC), the govermental body responsible for tracking infectious diseases, more than 85% of MRSA infections take place in healthcare facilities, making MRSA one of the most common nosocomial infection risks.

CA-MRSA is also known as community-acquired MRSA. This type of MRSA occurs in individuals in the community who are generally healthy and not receiving healthcare in a hospital or on an ongoing outpatient basis. In the last few years, there have been more and more outbreaks of this type reported in communities, meaning that MRSA infections are spreading out of hospitals and healthcare facilities and infecting the general public. Community health professionals are urging people to be more aware of MRSA as a growing threat.

EMRSA is also known as epidemic-type MRSA. A MRSA epidemic is defined differently in different countries. In the United Kingdom, for example, a MRSA epidemic occurs when two or more MRSA isolates are reported in two or more different medical facilities. In the United States, a MRSA outbreak is defined as either three or more nosocomially-acquired MRSA cases that are linked by some epidemiologic variable, or a drastic increase in the number of MRSA cases in a healthcare facility with endemic MRSA. A MRSA outbreak may be defined differently in different healthcare facilities.

Basic Features and Description

The most common type of MRSA infection is a skin infection, but this infection can affect other parts of the body or spread. In severe cases, MRSA infections may cause death due to septic shock or other complications of infection. Diagnosis of MRSA and testing for MRSA infections are described on the MRSA Diagnosis and Testing page in greater detail.

Methicillin-resistant Staphylococcus aureus infections may progress substantially within a day or two of the appearance of the first topical symptoms. MRSA infections are less likely to respond to treatment as the infection progresses. Usually, the initial symptom of the MRSA skin infection is small red bumps on the skin that may resemble pimples or spider bites, with or without fever. Within a couple of days, the bumps on the skin may get larger and become painful, eventually opening into deep, pus-filled boils.

If the infection has not spread too much, the MRSA infection can usually be successfully treated with antibiotic drugs. MRSA infections are defined by their resistance to the once-effective antibiotic drug methicillin. Over time, however, some strains of MRSA have evolved to become immune to other antibiotic drugs as well. This type of infection is called a multi-drug-resistant Staphylococcus aureus infection. Some strains of staph may be resistant to penicillin, methicillin, amoxicillin, oxacillin and some other antibiotics. While there is usually an antibiotic drug that can be used to destroy the bacteria causing the infection, Staphylococcus aureus is particularly good at adapting to new antibiotics. For more information about treatment of MRSA infections, see the MRSA Treatment page.

MRSA can cause serious problems when it spreads to other parts of the body. If MRSA infections involve internal organs, a patient may experience life-threatening complications. Regardless of whether a MRSA infection was acquired nosocomially or in the community, if the infection is not treated it can cause severe complications, such as: endocarditis, septic shock, osteomyelitis, necrotizing fasciitis and even death.