Management of a Concurrent Influenza A and Parainfluenza 1 Outbreak in a Residential Care Facility

To the Editor: There is significant risk of transmission of viral upper respiratory tract infections in residential care facilities (RCFs). Influenza A/B, parainfluenza, and respiratory syncytial virus (RSV) are common causes of outbreaks in RCFs.1 With emerging molecular assays for routine diagnostic testing, there is increasing recognition that infections and outbreaks may be the result of multiple viruses, although the clinical significance of identifying multiple pathogens is unclear.2, 3 Providence Health Care (PHC) comprises four RCFs and two acute care hospitals, with a microbiology and virology laboratory and an infection prevention and control (IPAC) team supporting all sites. In January 2014, an influenza-like illness (ILI) outbreak occurred in a PHC RCF (216 residents; 3 units). The approach of the IPAC team to the outbreak investigation and management of two concurrently circulating respiratory viruses resulting in mono- and co-infected patients is described herein. All residents with upper respiratory symptoms were investigated, with included cases defined as residents or staff with ILI (fever (>38°C) and cough) and one or more of sore throat, nasal congestion, malaise, chills, muscle aches, headache, and altered mental status.4 Afebrile residents with acute respiratory symptoms were included because fever may not be present.4 Centers for Disease Control and Prevention recommendations for outbreak management in RCFs were followed, and respiratory etiquette was reinforced.5 Oseltamivir prophylaxis was provided for residents and unvaccinated staff. Influenza vaccination coverage at this facility was 94% in residents and 83% in staff. Nasopharyngeal swabs were tested for respiratory viruses (in-house-developed multiplex polymerase chain reaction (PCR) assay: influenza A/B, RSV, parainfluenza 1/2/3, adenovirus, human metapneumovirus). The RCF staff notified IPAC when three residents in the same unit developed upper respiratory tract infection symptoms over a 24-hour period. PCR testing on the initial day of investigation confirmed parainfluenza 1 in all three residents, with outbreak precautions implemented on that unit only. Two further cases were positive for parainfluenza 1 and influenza A on Day 2. Because two respiratory viral pathogens were identified, all symptomatic residents were tested rather than case inclusion based on clinical and epidemiological evidence of a unit outbreak. Precautions were extended to the other two units over 5 days through active case finding: a resident on the second floor with influenza A (Day 3) and a resident on the third floor with parainfluenza 1 (Day 5). Outbreak cases are summarized as a bimodal epidemic curve (Figure 1). Twenty-eight residents manifested ILI symptoms, with 12 positive cases (7 parainfluenza 1, 2 influenza A, 3 parainfluenza 1/influenza A). Influenza cases (2/5) were subtyped as H1N1. Two residents had a fever. The median age of the cases was 94. The attack rate was 6%. There were no deaths or hospitalizations. Two healthcare workers (HCWs) developed ILI and were considered to be cases, but nasopharyngeal swabs could not be collected (sick leave). With no new identified cases for the 6 days after the onset of symptoms in the last case, the outbreak was declared over. In total, the outbreak lasted for 13 days. Viral respiratory outbreak management was revised in the context of two co-circulating viruses in two ways: respiratory virus testing and antiviral treatment. For this outbreak, after laboratory confirmation, microbiological testing was recommended for all symptomatic residents instead of inclusion of cases based on clinical symptoms,5, 6 which enabled decision-making regarding expanding unit closures to be based on microbiological confirmation rather than epidemiological case definitions. Without same-day rapid molecular testing, outbreak interventions may be too inclusive, resulting in excessive restrictions; alternatively, they could be too exclusive, potentially prolonging the outbreak because of delayed implementation of outbreak measures. All RCFs should consider rapid molecular testing to improve outbreak management. Quick laboratory confirmation of initial influenza cases facilitates optimal use of antiviral medication. Relying on epidemiological definitions may misidentify residents; the first three cases identified in this outbreak were positive for parainfluenza rather than influenza A. Effective chemoprophylaxis for influenza outbreaks depends on early initiation of oseltamivir, which would not have been initiated if only the initial cases had been tested. Reassessment of chemoprophylaxis duration may be considered in multivirus outbreaks. By testing all residents, persistence of circulating influenza can be monitored, and if only the noninfluenza virus is detected for two incubation periods after the onset of symptoms in the last resident with influenza, facility-wide prophylaxis could be discontinued.7 This may enable judicious use of antiviral agents, which can lead to cost savings and prevent the development of viral resistance.8 Multiplex PCR testing detected a dual-virus RCF outbreak, optimizing outbreak management, including antiviral stewardship. Microbiological confirmation of cases rather than epidemiological case finding should be considered when initial investigation identifies more than one viral pathogen. Preliminary results of this study were presented at IDWeek 2014, Philadelphia, Pennsylvania, October 8–12, 2014. Conflict of Interest: None of the authors have any relevant financial disclosures or conflicts of interest. Author Contributions: Badawi M., Leung V., Lowe C., Romney M. G., Gustafson R.: study concept and design. Pincock T.: acquisition of data. Lloyd-Smith E.: analysis and interpretation of data. Badawi M., Leung V., Lowe C., Romney M. G., Gustafson R.: preparation of manuscript. Sponsor's Role: No sponsor.

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