Counting Urinary Tract Infections for NHSN: Common Questions Answered

Hospitals that report to CDC's National Healthcare Safety Network (NHSN) track catheter-associated urinary tract infections (CAUTI), other urinary tract infections (UTI) and other urinary system infections using fixed surveillance definitions. NHSN answers the questions that infection preventionists most often ask about applying them. These are surveillance rules — designed to be applied the same way everywhere — not guides to diagnosis or treatment.

Which urine cultures qualify

• A count of at least 100,000 CFU/ml is required. If a laboratory reports ranges such as 75,000–100,000 and more than 100,000 CFU/ml, ask whether it can tell you that a culture had at least 100,000 CFU/ml and report it that way. If it cannot say for certain, don't use that culture for NHSN UTI surveillance.
• Mixed flora rules a culture out. A culture with one organism above 100,000 CFU/ml plus "mixed flora" cannot be used, because flora means a group of organisms — at least 2 more besides the one identified. The same goes for perineal, normal and vaginal flora.
• Organisms are counted to genus and species only. Two strains of E. coli count as one organism; different colony appearance or susceptibility results do not make separate organisms, because laboratories' methods differ. So E. coli #1, E. coli #2 and Staphylococcus aureus make two organisms, and the culture is eligible.
• Counts for the same organism are added together. In NHSN's example, three colony counts of Pseudomonas aeruginosa — 50,000, 50,000 and 10,000 colonies/mL — make 110,000, one organism above 100,000, and the culture is eligible. Where susceptibility panels differ, report the more resistant one.
• Separate cultures are not combined. More than 2 organisms in a single culture suggests contamination; that is not true of separate cultures each with fewer than 3. In NHSN's example, a culture with E. coli is considered first, and a later one with two other organisms can be considered if the first led to no UTI.
• Excluded organisms still count toward the total. A culture with Klebsiella oxytoca, Pseudomonas aeruginosa and a Candida species holds three organisms and is ineligible. A culture may contain an excluded organism such as Candida, but only alongside one other organism above 100,000 CFU/ml.
• Where the urine came from doesn't matter. Any urine specimen sent for culture can be reviewed against the criteria.

Which symptoms count

• Fever reported by the patient can be used when it is above 38.0°C and falls within the present-on-admission period and the infection window period of a positive culture. A general report of "fever" without a measured temperature cannot.
• Urinary retention is not dysuria. Dysuria means painful or uncomfortable urination, sometimes described as burning.
• Urgency, frequency and dysuria are hallmark UTI symptoms, and "no other recognized cause" does not apply to them. They can be used even on a day when a catheter was in place for part of the day, as long as the catheter was out when the symptom occurred. A symptom outside the infection window period can be used later if it is reported again within it.
• Costovertebral angle pain or tenderness: general "low back pain" does not count, since it has many causes, but lower back pain or flank pain on the left, right or both sides does.
• Suprapubic tenderness: "abdominal pain" is too general; lower abdominal pain, or bladder or pelvic pain or discomfort, is acceptable.
• Patients who cannot report pain — those with spinal cord or brain injuries, or heavily sedated or ventilated — may be less well served by the criteria, which balance sensitivity, specificity and practicality. NHSN asks facilities to apply the criteria as written, to examine patients and to watch for non-verbal signs of pain; ventilation or sedation does not always mean a patient cannot express it. A newer definition for spinal cord injury–associated neurogenic bladder does not exclude patients or change CAUTI results; it exists to count such patients and inform future changes.

"No other recognized cause." A symptom within the infection window period of a positive culture — often collected because a UTI was suspected — is presumed to relate to it. To set it aside, it should be clear that the symptom comes from another cause, one arising during the current admission. Ideally a physician or designee with access to the whole record makes that call, and it must be defensible and backed by physician documentation in case the case is validated.

Which patients and devices are included

• Leg bags and urometers. Patients whose catheters are switched from bed bags to leg bags for physical therapy, or opened to attach urometers in intensive care, stay in CAUTI surveillance; both practices may raise infection risk.
• Fistulas and neobladders. Patients with colovesical, enterovesical, urethrocutaneous or rectovesical fistulas, and patients with neobladders, are not excluded. A catheter in place puts them at risk, and the definitions already account for contamination by excluding cultures with more than 2 organisms.
• Several catheters. NHSN measures the risk of device use in general, not of a particular device, so a CAUTI is attributed to the inpatient location where the patient was on the date of event, never to a specific catheter.

Repeat infections, bloodstream infections and CMS

• Repeat Infection Timeframe (RIT). Once an event fully meets NHSN criteria, an RIT begins during which another UTI is not reported; the rules are in chapter 2 of the NHSN manual, "Identifying Healthcare-associated Infections."
• Secondary bloodstream infections. A bloodstream infection can be attributed to a UTI only if at least one organism in the blood matches an organism used as an element in meeting the UTI criterion, and the blood specimen falls within the secondary attribution period. If a UTI is met with E. coli above 100,000 CFU/ml, and the same culture had 50,000 CFU/ml of MRSA, a bloodstream infection with MRSA alone cannot be attributed to it.
• Reporting to CMS. Only catheter-associated UTI data — asymptomatic bacteremic UTI (ABUTI) and symptomatic UTI — go to the Centers for Medicare & Medicaid Services' Hospital Inpatient Quality Reporting Program. ABUTI can occur with or without a catheter; an ABUTI in a patient whose catheter meets the device-associated rule is a CAUTI, reportable if CAUTI reporting for that location is in the facility's monthly plan.

Asking NHSN

For help with a UTI determination, NHSN asks for the admission date, catheter insertion and removal dates, collection dates and results of urine cultures with colony counts, collection dates and results of positive blood cultures, and UTI signs and symptoms with their dates — sent to nhsn@cdc.gov without any personally identifiable information.

Sources

• Centers for Disease Control and Prevention, National Healthcare Safety Network, "FAQs: Urinary Tract Infection (UTI) Events": https://www.cdc.gov/nhsn/faqs/faq-uti.html
• Rewritten in hubnx's own words.
• The source's Fahrenheit equivalent for the fever threshold is misprinted, so only the Celsius value is given.