Methicillin-resistant Staphylococcus
aureus - Prevention and Control
by
Raymond B. Otero, Ph.D.
Consultant
After completing this educational format, the participant will be able to:
1. Discuss the general characteristics of MRSA such as transmission, incubation period and period of communicability;
2. Identify the common reservoir for MRSA;
3. Discuss how to accurately interpret microbiology reports in order to differentiate MRSA infection from MRSA colonization;
4. List two preventive and control measures for MRSA;
5. List the most common disinfectant for cleaning rooms containing MRSA infected patients.
Colonization - any person who is found to be culture positive for a specific organism such as Staphylococcus aureus, but has no signs or symptoms of infection caused by that organism. The organism source was from a patient or another human;
Carrier - an individual who is found to be persistently colonized (culture positive to a specific organism at one or more body sites such as anterior nares, perineum and throat, but has no signs or symptoms of infection;
Cohort - two or more colonized or infected residents with a particular organism such as methicillin-resistant Staphylococcus aureus who are separated physically (e.g. , separate rooms or wards) from other patients or residents with the same organism;
Disinfection - the destruction of organisms on inaminate surfaces using chemicals or physical (heat) agents;
Endemic - baseline rate or ongoing frequency of infections or colonization that may occur in a clinical setting such as a hospital or nursing home;
Epidemiology - the study of the relationships between various factors that determine the frequency and distribution of diseases in humans and other populations;
Infection - when an organism enters a body site and multiplies in tissue, it may or may not cause clinical manifestation of disease such as fever, suppurative drainage, inflammation, or tissue destruction. However, an individual can produce an immune response without clinical signs or symptoms. For example, a person who converts to a positive PPD skin test has been infected with tuberculosis. It does not necessarily mean that clinical disease is present. Many individuals may indicate in their health records that they never had chicken pox. However, a serological test may prove otherwise;
Morphology - the science that is concerned with the configuration or arrangement of organisms;
Toxins - poisonous substances produced by some organisms to enhance their ability to cause disease.
The incidence of methicilln-resistant Staphylococcus aureus has increased in healthcare facilities in the United States since the mid-1970’s. Approaches to the control of this organism since the realization of the problems of prevention and treatment were understood varied in their intensity among hospitals and nursing care facilities. All types of physical defense measures were applied to prevent the spread of the organism which comprised from strict isolation protocols in the late 1980’s to early 1990’s to the more sensible standard precautionary measures which have been recommended today by a variety of agencies including the Centers for Disease and Prevention (CDC).
The acronym MRSA stands for methicillin-resistant Staphylococcus aureus. It is important to note that clinical laboratories do not use the methicillin antibiotic for direct susceptibility testing (often referred to incorrectly as sensitivity testing). Methicillin is an antibiotic which is sensitive to physical pressures like temperatures. A 2o C change in temperature can result in a false negative reaction. A more stable antibiotic known as oxacillin is the common drug of choice for testing. Oxacillin-resistance when it occurs under appropriate laboratory testing indicates that a strain of Staphylococcus aureus is resistant to methicillin (MRSA).
The greatest concern is the limited choice of antibiotics for treatment. Vancomycin given IV is the only drug of choice for treating infected cases. It is important to note that vancomyin given appropriately will not eliminate colonization. You have to assume that the patient is probably still colonized with MRSA even after effective treatment has been completed.
Another major concern is the possibility of isolation due to the uncontrollable drainage of the infection or poor hygienic behavior of the patient which causes great concern and anxiety to the immediate family members. It is important for all hospitals and nursing homes to develop a protocol which will determine which type of patient requires isolation (private room). This will be discussed later.
- Shape - coccus (sphere) - Figure 1
- Morphology - clusters (grape-like) - Figure 1
- Gram reaction - positive - Figure 1
- Cultural characteristics - grows at 35 C and produces recognizable colonies within 16 - 18 hours of growth. Blood agar plates are commonly used to isolate the organism from clinical samples - Figure 2
- Coagulase activity - this organism coagulates rabbit plasma which is a differentiating test to separate other species of staphylococci - Figure 3
- Susceptibility to disinfectants and antiseptics - even though this organism can demonstrate multiple drug resistance to antibiotics, its sensitivity to disinfectants and antiseptics remains the same. Low level disinfectants such as quaternary ammonium chloride compounds are generally used to clean rooms that contain MRSA infected patients. MRSA strains are also very susceptible to antiseptics such as alcohol and iodine compounds.
NOTE: It is impossible to distinguish methicillin-susceptible from methicillin-resistant strains of Staphylococcus aureus clinically. Culture and susceptibility testing must be performed on all isolates of S. aureus regardless of anatomical source.
Figure 1 - Gram stain showing Gram positive intracellular cocci.
Figure 2 - Colonies of S. aureus on a blood agar plate.
Figure 3 - Coagulase test (conventional) - a negative test shows
no coagulation; a positive test demonstrates clotting.
Staphylococcus aureus produces a wide variety of enzymes and toxins. The ones listed below are some examples. It is important to note that not all strains of S. aureus produce these enzymes or toxins simultaneously.
- Coagulase - an enzyme that produces fibrin (all strains of S. aureus produce this enzyme).
- Hemolysins - an enzyme that destroys red blood cells.
- Hyaluronidase - an enzyme that destroys hyaluronic acid, an important constituent in connective tissue.
- Leukocidins - an enzyme that destroys white blood cells.
- Lipases - an enzyme that breaks down fatty acids.
- Enterotoxins - a toxin that causes food poisoning.
- Nucleases - an enzyme that breaks down nucleic acids.
- Exfoliatin - a substance that causes shedding of the superficial layers of the skin.
1. Folliculitis - infection of a hair follicle.
Figure 4 - Folliculitis - superficial folliculitis is essentially a staphylococcal impetigo in which a small area of erythema develops around a hair follicle and subsequently becomes a dome-shaped pustule.
2. Carbuncle - deep seated pyogenic (pus-producing) infection of the skin and subcutaneous tissue.
Figure 5 - Carbuncle - a deep-seated pyogenic infection of the skin and subcutaneous tissues.
3. Impetigo - a contagious superficial pyoderma (any pyogenic infection of the skin) often caused in conjunction with Streptococcus pyogenes.
Figure 6 - Impetigo - a contagious superficial pyoderma, caused by S. aureus and Streptococcus pyogenes, that begins with a superficial flaccid vesicle which ruptures and forms a thick yellowish crust, most commonly occurring in the face.
4. Mastitis (inflammation of the breast) - occurs in 1 - 3% of nursing mothers.
Figure 7 - Mastitis - infection often caused by Staphylococcus aureus in a lactating mother in a newborne nursery.
5. Wound infections.
6. Osteomyelitis - bone infection.
7. Food poisoning - usually occurs 2 - 6 hours after ingestion of food containing high concentration of carbohydrates such as custard filled bakery, potato salads and ice cream.
8. Toxic shock syndrome - a severe illness characterized by a sudden onset of high fever, profuse watery diarrhea, myalgia, followed by hypotension and, in severe cases shock. Typically occurring in young woman ages 15 - 25 using tampons. Starts abruptly during menses.
9. Scalded skin syndrome - most commonly in children and neonates. Starts abruptly with perioral (around the mouth) erythema with sunburn-like rash rapidly turning bright red spreading to bullae (large vesicle appearing as a circumscribed area) in 2-3 days and desquamating (peeling) within 5 days.
Figure 8 - Scalded skin syndrome
10. Septicemia/endocarditis - associated with age extremes, cardiovascular disease, diabetes, and heroin addicts.
11. Pneumonia - rare event with S. aureus unless preceded with influenza pneumonia or aspiration.
12. Neonatal skin lesions - sometimes occurring in hospital nurseries. Often attributed to hospital staff members (poor handwashing practices) or vaginally colonized mothers.
Figure 9 - Neonatal skin lesions
The incubation period (the time period that the organism gains entry into a patient until the appearance of the first sign(s) of symptom(s) or infection) for S. aureus infection is variable and indefinite. Occurs commonly around 4 - 10 days.
Common reservoir for Staphylococcus aureus including MRSA is primarily humans. Other animals are rarely involved.
- Laboratory input
As a nurse, it is particularly important that you are able to interpret microbiology reports. For example, there are four areas on a patient's microbiology final report form that must be carefully examined:
- Anatomical location - Is it written correctly? (i.e., right ankle drainage and not just drainage)
- Gram stain report - Gram stain reports should be requested for all wound lesions, internal fluids and lower respiratory secretions (look for the presence of WBC’s which indicate infection or epithelial cells which indicate upper respiratory secretions (spit) for sputum specimens.
- Organism - Is it important for nurses to know the epidemiology of the organism isolated such as source, modes of transmission, potential for multiple drug resistance.
- Antibiogram - What antibiotic is the organism susceptible or resistant to such as oxacillin, vancomycin (i.e., vancomycin-resistant Enterococcus faecalis), or penicillin (i.e., penicillin-resistant Streptococcus pneumoniae).
Examples of microbiology reports
- Anterior nares
Moisten a swab with bacteriostatic-free saline. Explain to the patient what you are going to do. Place swab into the left nares and rotate it gently for 3 - 5 seconds. Repeat with the right nares with the same swab. Place swab in a swab-culture transport system and tell the laboratory by way of the requisition form that you are looking for MRSA only.
- Infected area
The best specimen to submit from a suppurative lesion is a biopsy of the tissue or aspirated fluid. If neither method of procurement can be performed by the health care facility, then a swab is used. However a swab is not the best vehicle to use to determine infection because of surface contamination and small volume of material obtained (<0.2 ml).
Decontaminate area suspected of infection with 2x2’s and sterile bacteriostatic-free saline. As you are cleaning the area look for drainage material. Place two swabs simultaneously in the area of drainage and twirl gently absorbing as much material from the site as possible. Place one of the swabs in a swab-culture transport system and mark it for culture. Take the other swab and place it in a different swab-culture transport system and mark it for Gram stain.
The barriers required are gloves and gowns if soiling is likely. There is no need to wear a mask. Remember to place all contaminated items into a bag and remove them from the patient room and place in the appropriate disposal area. Remember to follow your facility’s waste disposal policy.
Since Staphylococcus aureus colonizes the anterior nares, auto-infection (Figure 11) is responsible for many infections that occur in a health-care and community setting. Patients with purulent drainage that can not be contained are the most common source of possible epidemic spread. Airborne transmission is rare. Fomite (inanimate objects) is also rare. Health-care workers can contribute to the spread of S. aureus if they do not perform common hygienic behavior (i.e., washing of hands, wearing gloves).
Figure 11 - Classical example of a Staphylococcus aureus auto-infection caused by poor hygiene and scratching
- Laboratory’s role
- Utilize the best detection methods available and rapid turn-around time for reports.
- Provide educational forums.
- Alert healthcare personnel when a MRSA isolate is cultured.
- Physician’s role
- Requesting the proper specimens.
- Not treating colonized patients with vancomycin
- Act as a resource person.
- Nurse’s role
- Able to interpret microbiology reports.
- Know the difference between colonization and infection.
- Communicate findings to physicians as soon as possible.
- Handwashing
Personnel should wash their hands after contact with patients regardless if gloves are worn. The use of an antimicrobial soap remains controversial. This measure is based on the assumption that soaps that contain antimicrobial agents will remove MRSA from the skin more effectively than standard soap. There is little convincing evidence that this practice is necessary, and its cost-effectiveness has not been established. It is not what you wash your hands with - it is when and how you wash your hands that is most important.
- Masks
The use of masks for caring for a patient with MRSA pneumonia is based on the assumption that S. aureus can be spread by droplet transmission (similar to tuberculosis). There is little evidence to support that S. aureus creates this type of aerosol. Masks are not generally recommended for this type of patient or burn patients.
- Housekeeping practices
Use common housekeeping practices for environmental cleaning (facility's procedures) of a room containing a MRSA infected patient. Common disinfectants such as quaternary ammonium compounds can used for general cleaning. Phenolics or hypochlorite solutions are unnecessary.
- Laundry and personnel clothing of infected MRSA patients
There is absolutely no need to wash any linens or clothing separately containing suppurative material from an infected MRSA patient. The normal processing of linen, i.e., temperature of water, detergents, sours (to reduce the alkali pH to a slightly acid condition in order to match human skin's pH), rinsing and drying will eliminate this organism from such materials.
- Dietary dishes
There is absolutely no need to use disposal dishes for someone who is infected with MRSA. The normal processing of dishes will eliminate this organism.
- Common-use equipment
Patients who require whirlpools and foot baths should not be denied this service because they have an infection caused by MRSA. There is no need to delay this service until the end of the day or week to allow other patients to use these types of equipment first. Follow the procedures for cleaning as recommended by the manufacturer. You can place an infected MRSA patient any time during the day in common-use equipment regardless of the number of uninfected patients schedule to use them.
- Microbiological cultures
Under no circumstance should a healthcare facility submit routine environmental cultures to determine if MRSA is in the area. Unless epidemiological data strongly suggests that such items were responsible for spread, environmental cultures should be discouraged.
To isolate a patient who is infected with MRSA the following criteria should be used:
- Can the infection be contained with proper dressing?
- Is the hygiene of the patient questionable?
- Does the patient have mental competence?
- Can the patient comply with appropriate handwashing procedures?
- Can the staff comply with Standard Precautions?
If a private room can not be obtained for isolation and a potential roommate is required for placement, the following criteria should be used:
- Does the potential roommate have any of the following:
- open wounds [ ]
- tracheostomy [ ]
- NG tube [ ]
- G-tube [ ]
- indwelling Foley catheter [ ]
- IV sites [ ]
If the answer to any of the above is yes [x], this is not a potential roommate.
If there is an already known colonized or infected patient, then cohorting would be the most logical procedure.
Contact isolation (private room) is the preferred method of containment for a patient who is infected with MRSA. This is based on the assumption that the drainage can not be contained and the hygiene of the patient is suspect.
There is absolutely no need to work restrict staff members who carry MRSA in their nares or other sites unless they have skin lesions or hygiene is suspect.
Sometimes a patient has recurrent infections caused by MRSA. The physician should be knowledgeable in the combination therapy that is required if decolonization is going to be attempted. It is important to note here that decolonization does not always work. The patient is being subjected to more antibiotics which could cause other factors such as elimination of indigenous flora (giving rise to Clostridium difficile pseudomembraneous colitis) or development of more resistant organisms.
MRSA is a contact organism. Standard precautions (formerly known as Universal Precautions) when followed, should control the spread of this organism. It is important that all members of healthcare facilities be in-serviced on the epidemiology of Staphylococcus aureus as well as other organisms such as vancomycin-resistant Enterococcus sp. that are endemic to an institution. This document that you have just read should be placed on all nursing stations so that the epidemiology on MRSA is fully understood.
References:
- CDC, 1998. Internet.
- Infectious Disease Handbook. Pp. 195-201. 1995-1996.
- Boyce, J.M., et. al., Methicillin-resistant Staphylococcus aureus (MRSA): a briefing for acute care hospitals and nursing facilities. Infection Control and Epidemiology. 15(2):105 - 115. 1994.
- Control of Communicable Diseases Manual. Benenson, A. S. , Editor. American Public Health Association. Pp. 428-438. 1995.
- Infectious Diseases. Gorbach, S. L., et. al., 2nd Edition. W. B. saunders. 1998.
- Wenzel, R. P., et. al., Methicillin-resistant Staphylococcus aureus outbreak: A consensus panel's definition and management guidelines. American Journal of Infection Control. 26(2):102-110. 1998.
All Material Copyright © Raymond B. Otero,
Ph.D., All Rights Reserved. |
