Spread of methicillin-resistant Staphylococcus aureus in a large tertiary NICU: network analysis

Abstract

Objective: Methicillin-resistant Staphylococcus aureus (MRSA) colonization in NICUs increases the risk of nosocomial infection. Network analysis provides tools to examine the interactions among patients and staff members that put patients at risk of colonization.

Methods: Data from MRSA surveillance cultures were combined with patient room locations, nursing assignments, and sibship information to create patient- and unit-based networks. Multivariate models were constructed to quantify the risk of incident MRSA colonization as a function of exposure to MRSA-colonized infants in these networks.

Results: A MRSA-negative infant in the NICU simultaneously with a MRSA-positive infant had higher odds of becoming colonized when the colonized infant was a sibling, compared with an unrelated patient (odds ratio: 8.8 [95% confidence interval [CI]: 5.3-14.8]). Although knowing that a patient was MRSA-positive and was placed on contact precautions reduced the overall odds of another patient becoming colonized by 35% (95% CI: 20%-47%), having a nurse in common with that patient still increased the odds of colonization by 43% (95% CI: 14%-80%). Normalized group degree centrality, a unitwide network measure of connectedness between colonized and uncolonized patients, was a significant predictor of incident MRSA cases (odds ratio: 18.1 [95% CI: 3.6-90.0]).

Conclusions: Despite current infection-control strategies, patients remain at significant risk of MRSA colonization from MRSA-positive siblings and from other patients with whom they share nursing care. Strategies that minimize the frequency of staff members caring for both colonized and uncolonized infants may be beneficial in reducing the spread of MRSA colonization.

FIGURE 1

Schematic diagrams of some of the patient ties (connections) analyzed. Room numbers correspond to physical locations of rooms relative to one another (that is, room 1 is immediately next to room 2, whereas there are 3 rooms between rooms 1 and 5). Details of tie definitions are presented in the text. Pt indicates patient; RN, nurse. A, Black lines represent ties between patient 1 and 4 other patients who were in the NICU with patient 1. From the perspective of patient 1, patient 4 is a roommate, patient 2 is 1 room away, patient 5 is 2 rooms away, and patient 3 is >2 rooms away. B, Patients 2 and 3 are connected through a direct nursing connection (red circle). As a result, indirect nursing connections (dotted lines) exist between patient 3 and patients 1, 4, and 5, because they are all within 1 room of patient 2. C, The normalized group degree centrality in this diagram is 0.33, because only 1 of 3 possible direct nursing connections exists between MRSA-negative infants (yellow text) and ≥1 MRSA-positive infant (red text).

FIGURE 2

Effect of physical distance between ego and alter on the risk of MRSA colonization. Bars represent 95% CIs around estimated ORs for an ego becoming MRSA-positive when an alter at a given distance is MRSA-positive instead of MRSA-negative.