Description of index case and exposure setting

A 54-year-old, foreign-born, HIV-negative nurse was diagnosed with cavitary pulmonary TB in January 2015 after experiencing nonresolving cough for 5 weeks. She was known to be PPD positive (30 mm) for more than 20 years, and her baseline chest radiograph showed right-sided apical changes. Treatment for LTBI had been offered but was declined on numerous occasions. The most proximate screening for symptoms of active TB was performed 5 months prior to the onset of the cough. Chest x-ray at time of diagnosis showed a large, right-sided, cavitary lung lesion. Sputum examination was strongly positive for acid-fast bacilli by smear (3+), and culture from sputum grew isoniazid (INH)-resistant MTB after 14 days of incubation.

The index case HCW was assigned to cover a single inpatient unit as part of her daily assignments. She used isolation precautions for every patient following routine care standards. This unit is a 42-bed inpatient ward with 10 private rooms, including a single airborne infection isolation room; the remaining 16 rooms house 32 beds. The air-handling system on the unit allows 8 air changes per hour and incorporates a high-efficiency particulate air filtration system (99.97% retention). Patients admitted to the unit are surgical and medical cases, predominantly with head- and neck-related cancer diagnoses. Only patients who had direct contact with the index case HCW were considered at risk.

Contact tracing

A multidisciplinary response team was assembled including representatives from infection prevention, employee health, nursing, clinical laboratories, health informatics, and administration. The contagious period was calculated based on the onset of cough until the last contact on the unit, as previously described. ¹⁹

Nursing informatics created a logic-based query to identify all patients for whom any documents had been authored by the index case HCW within the 3-month contact-tracing period from the electronic medical record system (EMR). Any interaction that would require a face-to-face encounter with a patient was built into the query. These encounters covered all aspects of nursing care: nursing admission and daily assessments, patient education, recording event notes, obtaining vital signs, and medication administration. Based on these encounters, patients that received direct care from the index case HCW were initially identified. Next, time spent providing direct patient care was derived to estimate exposure times and cumulative risk (in hours) (Table 1).

TABLE 1

Interactions Based on Tracing of Documents Authored by the Index Case From Electronic Medical Records and Estimate Exposure Time for Each Event

A concentric-circle approach was used; significant exposure for those included in the first tier was further refined by the susceptibility of the exposed patient (ie, underlying cancer type, positive HIV status, or transplant recipient). For patients with solid tumors, 2 interactions performed by the index HCW with an estimated cumulative exposure time of ≥2 hours were considered significant. For those with underlying hematologic malignancy, stem-cell transplant recipients, or HIV-positive persons, any direct care was considered substantial exposure and was included in the first tier. ²⁰

For HCWs, first-tier exposure lists were created using the nursing schedule and the EMR to identify coworkers with overlapping shifts. Any HCW sharing any part of a work shift, defined by ≥8 hours of shared time on the same unit with the index case HCW during the contagious period, was considered to have had significant exposure.