Healthcare facilities use several screening tests for infection control, with the specific test depending on which pathogen they’re trying to detect. The most common are nasal swabs for MRSA, rectal swabs for drug-resistant gut bacteria, skin swabs for emerging fungal threats, and stool testing for C. diff. These tests fall into two broad categories: traditional culture methods, which grow bacteria on plates in a lab, and rapid molecular tests like PCR, which detect pathogen DNA directly and return results much faster.
MRSA Nasal Screening
Methicillin-resistant Staphylococcus aureus is one of the most commonly screened pathogens in hospitals. Screening typically involves swabbing the inside of the nose (the nares), since MRSA colonizes there even in people who show no symptoms. The swab is then tested using either a culture method or a PCR-based rapid test.
Culture-based detection involves placing the swab sample on an agar plate that contains specific antibiotics. If MRSA is present, colonies grow within 24 to 48 hours. PCR testing, by contrast, can identify MRSA genetic material in as little as a few hours. Both approaches are reliable, but the speed of PCR makes it more practical when isolation decisions need to happen quickly, such as on admission to an intensive care unit.
Preoperative MRSA screening is a particularly well-established practice. Guidelines from the Society for Healthcare Epidemiology of America recommend screening surgical patients before high-risk procedures, especially orthopedic and cardiothoracic surgeries. When a patient tests positive, a decolonization protocol typically starts three to five days before surgery, using an antibiotic ointment applied inside the nose and antiseptic body washes. This combination significantly reduces the risk of surgical site infections.
Screening for Drug-Resistant Gut Bacteria
Carbapenem-resistant Enterobacterales (CRE) are among the most dangerous drug-resistant organisms in healthcare settings, and clinical cultures alone catch only a fraction of colonized patients. To find carriers who aren’t visibly sick, facilities collect rectal or perirectal swabs and culture them on selective media that allow only resistant bacteria to grow.
The CDC defines CRE as gut bacteria resistant to carbapenem antibiotics, a class typically reserved as a last resort. Detecting whether these bacteria produce a specific resistance enzyme (carbapenemase) matters because enzyme-producing strains spread resistance more easily. Acceptable tests for this include PCR, the Carba NP biochemical test, and other specialized assays. When a case is identified, facilities are encouraged to screen epidemiologically linked contacts, such as roommates, using at minimum a rectal swab culture.
Candida Auris Detection
Candida auris is an emerging fungal pathogen that poses unique screening challenges. No simple physical or growth characteristics reliably distinguish it from other yeast species, which means standard yeast identification methods can easily misidentify it. The CDC notes that the most reliable identification method is a technology called MALDI-TOF mass spectrometry, which identifies organisms based on their protein signatures.
For screening colonized patients, skin swabs (typically from the armpit and groin) are the standard specimen. Real-time PCR is the preferred detection method. Facilities are encouraged to begin screening patients after an initial case is identified, focusing on those who shared the same unit or had overlapping care teams.
C. Diff Testing Algorithms
Clostridioides difficile testing works differently from most infection control screening because it’s typically ordered for patients already showing symptoms, particularly watery diarrhea. Rather than a single test, many labs use a multi-step algorithm to balance speed and accuracy.
The first step is often a rapid antigen test that detects a protein called GDH, which C. diff produces in large quantities. This test takes less than an hour but only confirms the organism is present, not that it’s producing harmful toxins. A positive antigen result is then followed by either a toxin test (an enzyme immunoassay that detects the actual disease-causing toxins) or a PCR test that confirms the presence of toxin-producing genes. PCR is highly sensitive and specific, returning same-day results. Using these tests in combination prevents both false positives and unnecessary treatment.
Vancomycin-Resistant Organisms
Vancomycin-resistant enterococci (VRE) screening also relies on rectal swabs, since these bacteria colonize the gut. The lab places the specimen on agar plates containing vancomycin. If bacteria grow despite the antibiotic’s presence, they’re resistant. For S. aureus strains with vancomycin resistance (a rarer and more alarming finding), the CDC recommends a vancomycin agar screen plate using brain heart infusion agar containing a set concentration of vancomycin. Laboratorians inoculate the plate and incubate it at body temperature for a full 24 hours, examining closely for any sign of growth.
PCR vs. Culture: Speed and Accuracy
The fundamental tradeoff in infection control screening is between traditional culture and molecular (PCR) testing. Culture remains the gold standard for confirming a living, viable organism and testing which antibiotics work against it. But it’s slow. PCR is fast and highly sensitive, detecting pathogen DNA within hours rather than days.
A 2024 clinical study comparing the two approaches for complicated urinary tract infections found that PCR-guided treatment produced better clinical outcomes than culture-guided treatment (88% vs. 78% success rate), with an average turnaround time of about 50 hours compared to 104 hours for conventional culture and sensitivity testing. That time difference matters enormously in infection control, where every hour a colonized patient goes unidentified is an hour they could transmit a resistant organism to others.
Many facilities now use PCR for the initial screening decision (whether to isolate a patient) and follow up with culture when they need detailed antibiotic susceptibility information.
Universal vs. Targeted Screening
Hospitals can screen every patient on admission (universal screening) or focus on those with specific risk factors (targeted screening). The right approach depends on how widespread the pathogen already is in a region and what type of facility is involved.
CDC modeling shows that at early stages of an outbreak, screening admissions at high-influence facilities like long-term acute care hospitals and ventilator-capable skilled nursing facilities has the greatest impact on regional spread. These facilities tend to care for sicker patients who are more likely to carry resistant organisms. At later stages, when a pathogen is more established in a region, screening at large acute care hospitals that discharge patients to many other facilities becomes more impactful, because those hospitals act as dispersal hubs.
Targeted screening focuses on patients with known risk factors: those who are bedbound, receiving antibiotics, on mechanical ventilation, requiring high levels of care, or transferring from facilities with known outbreaks. This approach uses fewer resources while still catching a large proportion of carriers. The Joint Commission requires accredited hospitals to develop surveillance programs based on their geographic location, the populations they serve, and infection control data, giving individual facilities flexibility to tailor their screening strategies.
Visitor and Staff Screening
Screening isn’t limited to patients. The CDC’s updated 2024 draft guidelines for preventing pathogen transmission in healthcare settings address visitor symptom screening as a tool to reduce healthcare-associated infections, particularly in high-risk areas like oncology wards and neonatal intensive care units. This screening can be passive (signs posted at entrances asking symptomatic visitors to stay away) or active (staff asking visitors about current symptoms and recent exposures before allowing entry). During periods of high community respiratory virus transmission, facilities may also implement source control measures such as requiring masks for healthcare personnel during patient interactions or for everyone entering a clinical area.