Methicillin-resistant Staphylococcus aureus (MRSA) is a type of Staphylococcus bacteria resistant to several common antibiotics, including methicillin. Many people carry this bacteria harmlessly on their skin or in their nose, but it can cause serious infections if it enters the body through a break in the skin. The primary goal of swabbing is to screen for colonization—identifying carriers before a procedure like surgery—or to diagnose an active infection. Performing the swab correctly ensures the laboratory receives a viable sample necessary for accurate results that guide infection control and treatment decisions.
Essential Supplies and Preparation
Preparing the necessary materials ensures a successful and uncontaminated sample collection. The specialized swab is typically a flocked type, which uses fine nylon fibers to maximize the collection and release of cells, offering superior performance compared to standard cotton swabs. This swab is paired with a transport tube containing a liquid medium, such as Amies, which keeps the bacterial sample alive and intact until it reaches the lab for analysis.
Before collection, strict hand hygiene must be performed, and clean gloves should be worn to protect the sample from external contamination. All materials, including the swab, transport tube, and patient labels, should be assembled on a clean surface. The label containing the patient’s identification and the sample source must be ready to affix immediately after collection to prevent mix-ups.
Standardized Collection Sites and Procedure
MRSA swabbing is performed for two purposes: screening for colonization and diagnosis of an active infection, which determines the collection site. Screening protocols commonly focus on the anterior nares (nostrils) because the nasal passage is the most frequent site where Staphylococcus aureus colonizes the body. The procedure requires the swab to be inserted approximately one to two centimeters into the nostril.
Once the swab tip is inside, gently rotate it against the inner wall of the nostril for about five rotations over a period of up to 15 seconds. This rotational technique scrapes epithelial cells and residing bacteria from the mucosal surface without causing discomfort. Crucially, the same swab is then used to repeat the exact procedure in the second nostril to ensure a comprehensive sample is collected from the primary colonization site.
Other sites may be swabbed for screening, particularly in healthcare settings, including the groin, axilla (armpit), or perineum. For a groin swab, the tip is gently rolled over the skin folds where the thigh meets the torso, using one swab for both sides. These secondary sites are checked because they are warm, moist areas where the bacteria can also comfortably reside.
Diagnostic swabbing focuses on a specific site of suspected infection, such as a wound, skin lesion, or surgical site. When swabbing a wound, the collector must focus on the active, advancing edge rather than the center, which may contain only dead tissue or pus. Isolating the bacteria from the actively infected area provides the most accurate picture of the organism causing the illness. After collection, the swab shaft is carefully broken at the designated breakpoint before sealing the transport tube.
Post-Collection Handling and Result Interpretation
Once collected, the swab tip must be immediately placed into the transport tube and sealed securely to prevent leakage and maintain microorganism viability. The liquid medium preserves the bacteria during transport, ensuring the lab can successfully grow and identify the organism. The labeled tube is then sent to the laboratory, ideally within 24 hours if kept at room temperature, though refrigeration can extend the sample’s stability.
In the laboratory, the sample is tested using culture or molecular testing. Culture involves placing the sample on a nutrient-rich plate, allowing bacteria to grow, and then testing for antibiotic resistance, typically yielding results in one to two days. Molecular testing (PCR) detects specific genetic markers for MRSA, such as the mecA gene, and often provides results within a few hours.
A positive screening result indicates colonization, meaning MRSA is present but not causing an active infection. This information is used by healthcare providers to implement decolonization protocols or enhanced infection control measures, especially before surgery. Conversely, a negative result suggests MRSA is not present and is highly predictive that MRSA is not the cause of a patient’s current illness.