Present on Admission or Healthcare-Associated? NHSN's Surveillance Rules Explained

A patient's physician says there is no infection; the chart meets the National Healthcare Safety Network (NHSN) criterion anyway. Which wins? For NHSN — CDC's healthcare-associated infection (HAI) tracking system, the most widely used in the country — the answer is both: report the event, and never let a surveillance definition override clinical judgment. Here are NHSN's answers to the questions infection preventionists ask most often.

Surveillance is not diagnosis

• Surveillance definitions exist to study trends across a population. Applying the same criteria — and only those criteria — consistently is what makes pooled data trustworthy.
• Clinical diagnoses are about one patient and weigh all available clinical, epidemiological and laboratory data, including data NHSN does not use.
• So a clinical diagnosis can be made when a surveillance definition is not met, and vice versa. Failing to meet a surveillance definition should never impede clinical care, and failing to meet a clinical definition should never stop an infection that meets NHSN criteria from being reported.

Present on admission (POA) or healthcare-associated (HAI)?

For all infection types except VAE, PedVAE, SSI and LabID events, work in this order:

1. Find the diagnostic test — the date of the test that is an element of the NHSN site-specific criterion that is met. Specimen collection, an imaging test, or a procedure or exam count as diagnostic tests only when they are an element of that criterion.
2. Set the infection window period (IWP): the 3 days before the test, the day of the test and the 3 days after — 7 days in all. If the test falls on hospital day 3 or earlier, the days before it can reach back only into the POA timeframe, the 2 days before admission.
3. Check the criterion: if every element is met within the IWP, there is an infection event; if not, there is none.
4. Set the date of event (DOE): the date the first element used to meet the criterion first occurs within the IWP.
5. Decide: if the DOE falls in the POA timeframe — the 2 days before admission, the day of admission or the next day — the infection is POA. Otherwise it is an HAI.

Chapter 2 of the NHSN Patient Safety Component Manual, Identifying HAI for NHSN Surveillance, gives guidance and examples.

Physician diagnosis counts toward POA only when it is part of the site-specific criterion. The bloodstream infection (BSI) criteria do not include it, so a physician's note of BSI cannot meet them. Admitting diagnosis and treatment on admission, such as antibiotics, do not matter; only the DOE does.

MRSA on an admission screen does not meet an infection criterion. If the patient meets an NHSN definition on or after hospital day 3, report an HAI.

The repeat infection timeframe (RIT)

The RIT is a 14-day period, starting on the DOE, in which no new infections of the same type are reported. A POA infection sets one too. For surveillance, a POA infection's DOE can only be the day of admission to an inpatient location or the next day: if the first element occurred in the 2 days before admission, the DOE — and day 1 of the RIT — is the day of admission, hospital day 1.

Example: a symptomatic UTI with E. coli and a DOE on the day of admission is POA. If a new symptomatic UTI with K. pneumoniae appears 10 days later, K. pneumoniae is added to the original UTI, and the RIT stays hospital days 1–14.

A POA BSI followed by further blood specimens must be classified as primary or secondary. A primary POA BSI sets a BSI RIT; a secondary one sets an RIT only for the infection it is secondary to.

Signs, symptoms and tests

Documentation and pathogens

• Conflicting notes: NHSN takes all documentation at face value and as equally valid. Purulence documented on hospital day 4 can be used even if day 5 says "no purulence noted." NHSN cannot adjudicate conflicts; if a culture's label doesn't match its collection, the facility decides which is accurate.
• Pathogens: report up to three, most important first (usually the lab report's order), and all site-specific pathogens before secondary BSI pathogens. If the species isn't given or isn't in the NHSN terminology browser, choose the genus. Don't assume an organism missing from the browser is ineligible for a CLABSI — contact NHSN through ServiceNow or at nhsn@cdc.gov.
• COVID-19 (required for every HAI event): use the most recent viral test on or before the DOE — "yes" if the patient was lab-confirmed, "no" if that test was negative. There is no time limit on "confirmed"; the answer rests on the current hospitalization's record.

Counting patients and devices

• Patient ID: use one that stays the same across visits, such as the medical record number. An ID that changes each visit breaks the link between an SSI and its procedure and distorts LabID events and measures.
• Observation, swing-bed and hospice patients in an inpatient location are included in its HAI surveillance, denominators and LabID event surveillance.
• Device days: a device present for any part of a calendar day counts that day toward the more-than-2-day minimum for a device-associated infection — including removal and reinsertion the same or next day. If a full calendar day (not 24 hours) passes without the device, the count starts over; removed Monday and not reinserted until Wednesday or later, for instance.
• Denominators are collected at the same time every day in each location. Alternatively, count patients and patients with an indwelling urinary catheter, central line or ventilator on one designated weekday at the same time each week — never Saturday or Sunday — while still counting patient days daily. Only non-oncology ICUs and wards averaging 75 or more device days a month in the previous year may sample.
• One CCN, several facilities: the CMS certification number doesn't define enrollment. Physically separate facilities enroll separately, each with its own NHSN OrgID; physically connected buildings of one facility on one campus share a single ID. CDC combines data under a shared CCN for CMS reporting and still analyzes each facility separately.

Sources

Based on "FAQs: Miscellaneous," National Healthcare Safety Network, Centers for Disease Control and Prevention; a work of the United States government in the public domain. See also the NHSN Patient Safety Component Manual, chapter 2.