What is Methicillin-Resistant Staphylococcus aureus ?
Methicillin-resistant Staphylococcus aureus, or MRSA, is a type of bacteria that’s resistant to certain antibiotics. Doctors define it as being resistant to a type of antibiotic called oxacillin when the concentration of oxacillin needed to kill it is 4 micrograms/mL or more. MRSA is one of the top causes of infections caught in hospitals. These infections can cause serious health issues, potentially fatal, longer hospital stays, and larger costs.
There are two types of MRSA infection: hospital-associated (HA-MRSA) and community-associated (CA-MRSA). The two types are different in various ways, including their symptoms, the nature of the bacteria, and the antibiotics they are susceptible to, which can affect the treatment process.
What Causes Methicillin-Resistant Staphylococcus aureus ?
Methicillin resistance, or resistance to a certain type of antibiotic, happens in a bacterium called S. aureus through changes in a protein that binds to penicillin, a kind of antibiotic. This protein is encoded on the bacterium’s chromosome, part of its DNA. This resistance can be passed from one S. aureus bacterium to another through virus-like particles called bacteriophages. This is one of the few known instances in medicine where drug resistance is spread via virus-like particles in this way.
Risk Factors and Frequency for Methicillin-Resistant Staphylococcus aureus
The first case of MRSA infection, a type of bacterial infection, was identified in 1961. After that, the number of people affected by MRSA infection in the United States grew significantly. However, recent studies indicate a decrease in hospital-acquired MRSA cases, although community-acquired MRSA cases are on the rise. MRSA infection rates are reported to vary from 7% to 60%.
There are numerous risk factors associated with getting a MRSA infection. These include:
- Being hospitalized for a long time
- Being admitted to intensive care or a nursing home
- Recent use of antibiotics
- Undergoing invasive procedures
- Having HIV
- Having open wounds
- Undergoing hemodialysis
- Using a long-term central venous access or urinary catheter
- Being a healthcare worker who has direct contact with infected patients.
Although being older isn’t directly seen as a risk factor for MRSA, people over 65 years old are more at risk of hospitalization, and thus indirectly have a higher chance of acquiring MRSA. Similarly, living in an area with a high rate of community-acquired MRSA, or being admitted to a hospital with a high rate of hospital-acquired MRSA, increases the likelihood of exposure to MRSA.
Signs and Symptoms of Methicillin-Resistant Staphylococcus aureus
Staph bacteria, also known as MRSA, can cause various infections depending on which part of your body it affects. These infections range from minor skin infections to more severe problems such as meningitis or pneumonia. There’s also an increased risk of further complications and death if you’re a drug user and develop a heart infection (endocarditis) caused by MRSA.
Here are some specific ways MRSA can impact different areas of your body:
- Skin and soft tissue: Known for causing infections like cellulitis, necrotizing fasciitis, and diabetic foot ulcers, MRSA is usually resistant to multiple drugs, leading to frequent relapses and increased hospital stays. The risks associated with these infections also rise if MRSA is involved.
- Bone and joint: Staphylococci bacteria, including MRSA, are the leading cause of bone and joint infections. MRSA can lead to osteomyelitis (an infection in your spine, long bones of upper and lower extremities), either from a local wound infection or from an infection in the blood. It can also cause septic arthritis in both natural and artificial joints.
- Lungs: MRSA can cause staphylococcal pneumonia, which can have severe symptoms like high fevers, bloody cough, and low blood pressure, and can quickly advance to sepsis or septic shock. This infection, characterized by severe respiratory symptoms, is more commonly known to lead to hospital-acquired and ventilator-associated pneumonia. Both conditions involve pneumonia developing a couple of days after the start of a hospital stay or after being put on a ventilator, and both have a high risk for poor outcomes.
- Bloodstream: Bloodstream infections due to staph bacteria, including MRSA, have been linked to a death rate of 15% to 60%. This kind of infection is often seen in ICU patients with central lines and is related to poorer outcomes compared to other MRSA infections because of lower response rates to the antibiotic vancomycin.
- Heart: Finally, MRSA is a key cause of bacterial heart infections (endocarditis), and about a third of individuals with this infection could die. These infections are commonly seen with drug use and IV catheters, which can lead to further complications like septic pulmonary emboli (blood clots in the lung), or secondary infections in other body parts like bones and joints, kidneys, and brain. Careful history-taking, examination, and necessary tests are essential for dealing with such cases.
Testing for Methicillin-Resistant Staphylococcus aureus
If you are at risk for a specific type of bacterial infection called Methicillin-resistant Staphylococcus aureus (MRSA), your doctor will likely keep a close eye on your condition. This is important because starting treatment quickly makes a big difference. Even before test results are in, your doctor might choose to start you on antibiotic medication that treats MRSA.
If your doctor suspects that you may have MRSA, they will likely collect a sample from the area they think is infected. This could be blood, sputum (coughed-up mucus), urine, or a scrape from a wound to be tested in the lab.
One of the testing methods your doctor might use is a Gram stain test. If this test shows clusters of certain types of bacteria, it could hint at MRSA. Another test, the DNA polymerase chain reaction (PCR) test, is even more accurate. If the results of other tests are unclear, this PCR test is considered the best one to clear things up.
Doctors often take a sample from the inside of your nose to test for MRSA. While a positive result can show if you’re carrying the bacteria, it doesn’t necessarily mean you have an infection. But a negative result can be a strong sign that you’re not infected with MRSA.
When dealing with a possible MRSA infection in the lungs, tests on sputum may not be very reliable. Instead, your doctor might opt for different procedures like a bronchoalveolar lavage – a method that washes out your lungs and collects the washings for examination. For patients who are intubated (have a tube inserted into their airway) or have a tracheostomy (surgical opening in the windpipe), a deep
tracheal aspirate or sputum sample will be taken to help identify the bacteria.
Treatment Options for Methicillin-Resistant Staphylococcus aureus
Choosing the right antibiotic to treat a MRSA (methicillin-resistant Staphylococcus aureus) infection depends on a few factors. These include the kind of disease, the local resistance patterns of the bacteria, how easy it is to get the antibiotic, potential side effects, and individual patient characteristics.
For most simple skin and soft tissue infections (SSTIs) suspected to be caused by MRSA, doctors usually prescribe antibiotics like trimethoprim/sulfamethoxazole, doxycycline, or minocycline. Stronger doses of these antibiotics are recommended for severe MRSA cases. Other antibiotics like linezolid, tedizolid, and delafloxacin may also be used if they’re available and cost-effective.
Certain conditions like severe SSTIs, inadequate response to oral antibiotics, and infections near implanted devices may instead require antibiotics delivered directly into the bloodstream (parenteral antibiotics).
In a hospital setting, the go-to drug for MRSA infections is typically an antibiotic called vancomycin which is also given via IV. A small number of MRSA cases may be resistant to vancomycin, but it’s generally effective against most MRSA infections. If vancomycin can’t be used because of availability issues or side effects, other options include daptomycin, ceftaroline, telavancin, dalbavancin, and oritavancin. Based on culture and susceptibility data, doctors may adjust your antibiotic regimen.
Treatment durations can vary from 5 to 14 days depending on the severity of the infection and how you respond to the treatment.
In case of MRSA found in the bloodstream (bacteremia), the first course of action is to identify and control the source of the infection. Doctors typically use vancomycin or daptomycin as the initial treatment until they can determine which antibiotic the bacteria are susceptible to. In such cases, if the bacteria show resistance to vancomycin, daptomycin is considered a good alternative. Telavancin, and ceftaroline can also be used as alternatives if both vancomycin and daptomycin aren’t suitable. In difficult-to-treat cases, combinations of different antibiotics may be used.
Another antibiotic called teicoplanin, although not commonly used and not available in the USA, has also been found to be as effective as vancomycin, with fewer side effects. Certain other antibiotics like linezolid, quinupristin-dalfopristin, tigecycline, or fluoroquinolones are usually not recommended for treating MRSA in the bloodstream.
If you are being treated for MRSA in the bloodstream, your doctors will typically retest you to make sure the infection is cleared.
For MRSA-related heart infections (endocarditis), the 2015 American Heart Association (AHA) guidelines recommend IV vancomycin as the first line of treatment. Daptomycin is the suggested alternative for patients who cannot tolerate vancomycin. The treatment duration for a native heart valve infection is usually around six weeks. For an infection in an artificial heart valve, the treatment includes IV vancomycin and rifampin for 6 weeks, with the addition of gentamicin in the first 2 weeks of therapy. There’s no strong evidence that a mix of rifampin or gentamicin with vancomycin or daptomycin is more beneficial for native valve endocarditis. Other antibiotics like telavancin, ceftaroline, and quinupristin-dalfopritin can be used in specific situations if standard treatment doesn’t work. However, clindamycin or linezolid are not recommended because they don’t work as well as cell wall active agents like vancomycin and daptomycin.
What else can Methicillin-Resistant Staphylococcus aureus be?
There are several conditions that can occur in children, and these can range from infections to autoimmune diseases. Some of these include:
- Bacteremia (bacterial infection in the blood)
- Chemical burns
- Impetigo (a highly contagious skin infection)
- Juvenile idiopathic arthritis (a type of arthritis that occurs in children)
- Kawasaki disease (a rare childhood illness that involves inflammation of the blood vessels)
- Leptospirosis (a bacterial disease that affects humans and animals)
- Parvovirus B19 infection (a virus that can cause a variety of illnesses)
- Pediatric bacterial endocarditis (an infection of the inner lining of the heart)
- Pediatric osteomyelitis (an infection in the bone)
