This was a 20-week period when influenza was expected to be circulating. Most HCWs had been vaccinated against influenza A(H1N1)pdm09 virus
Nasal (not nasopharyngeal) swabs were collected by a trained staff member every 2-weeks, with extra swabs taken if a period of illness arose in the meantime. Nasopharyngeal swabs (NPS) do yield higher proportions of viral detections but are not pleasant and may have caused study drop-outs among the volunteers so they were not used.
Influenza viruses, respiratory syncytial virus, rhinovirus (RV), human metapneumovirus (HMPV), parainfluenzavirus (PIV), endemic coronavirus (HCoV), adenovirus, bocavirus and enterovirus shedding was represented by the presence of viral RNA detected using a commercial PCR assay (MultiCode-PLx-RVP). An internal control target, β-actin, was included to monitor the integrity of the extracted nucleic acids.
A PCR positive is assumed to represent shedding of an infectious virus.
The findings are relevant to my recent rant on prospective testing (seek and you shall find). Some key findings were:
- HCWs often worked despite being ill
- The strongest and most statistically significant risk of finding a virus in a subject was associated with that subject being symptomatic (I'm going to be writing about asymptomatic infections in the coming weeks)
- Only 42 specimens were positive for a virus - mostly RV (33) followed by PIV (4), CoV (4) and HMPV (1) - lower than expected
- Younger age was positively associated with viral shedding while the subject's role as a nurse or a physician was not
- 15% of RV detections were made from asymptomatic subjects - 25% of PIV or HCoV (OC43 and NL63) detections were from this group.
- 85% of RV detections were from symptomatic (ill) subjects
When you test for things, its amazing what gets found and how this can impact on policy, understanding of infectious disease transmission and improved patient management.
This is also a timely reminder that issues around infection prevention and control (IPC) are in no way limited to the management of newly emerged viruses like H7N9 or MERS-CoV. IPC is a problem the world over and it requires constant vigilance to stay ahead of. I commend the authors for this study.