Absence of detectable influenza RNA transmitted via aerosol during various human respiratory activities--experiments from Singapore and Hong Kong

PLoS One. 2014 Sep 10;9(9):e107338. doi: 10.1371/journal.pone.0107338. eCollection 2014.

Abstract

Two independent studies by two separate research teams (from Hong Kong and Singapore) failed to detect any influenza RNA landing on, or inhaled by, a life-like, human manikin target, after exposure to naturally influenza-infected volunteers. For the Hong Kong experiments, 9 influenza-infected volunteers were recruited to breathe, talk/count and cough, from 0.1 m and 0.5 m distance, onto a mouth-breathing manikin. Aerosolised droplets exhaled from the volunteers and entering the manikin's mouth were collected with PTFE filters and an aerosol sampler, in separate experiments. Virus detection was performed using an in-house influenza RNA reverse-transcription polymerase chain reaction (RT-PCR) assay. No influenza RNA was detected from any of the PTFE filters or air samples. For the Singapore experiments, 6 influenza-infected volunteers were asked to breathe (nasal/mouth breathing), talk (counting in English/second language), cough (from 1 m/0.1 m away) and laugh, onto a thermal, breathing manikin. The manikin's face was swabbed at specific points (around both eyes, the nostrils and the mouth) before and after exposure to each of these respiratory activities, and was cleaned between each activity with medical grade alcohol swabs. Shadowgraph imaging was used to record the generation of these respiratory aerosols from the infected volunteers and their impact onto the target manikin. No influenza RNA was detected from any of these swabs with either team's in-house diagnostic influenza assays. All the influenza-infected volunteers had diagnostic swabs taken at recruitment that confirmed influenza (A/H1, A/H3 or B) infection with high viral loads, ranging from 10(5)-10(8) copies/mL (Hong Kong volunteers/assay) and 10(4)-10(7) copies/mL influenza viral RNA (Singapore volunteers/assay). These findings suggest that influenza RNA may not be readily transmitted from naturally-infected human source to susceptible recipients via these natural respiratory activities, within these exposure time-frames. Various reasons are discussed in an attempt to explain these findings.

MeSH terms

  • Adolescent
  • Adult
  • Cough
  • Exhalation
  • Female
  • Hong Kong
  • Humans
  • Influenza A Virus, H1N1 Subtype / genetics*
  • Influenza A Virus, H3N2 Subtype / genetics*
  • Influenza B virus / genetics*
  • Influenza, Human / transmission
  • Influenza, Human / virology*
  • Male
  • Middle Aged
  • Models, Anatomic*
  • RNA, Viral / genetics*
  • RNA, Viral / isolation & purification
  • Respiration
  • Singapore
  • Viral Load

Substances

  • RNA, Viral

Grant support

Funding for the Hong Kong study was supported by the Area of Excellence Scheme of the Hong Kong University Grants Committee (grant no. AoE/M-12/06) and a RGC GRF grant (HKU7142/12). Funding for the Singapore study and support for post-doctoral research fellows ADN and CAK were provided by grants to JWT/ESCK from Singapore’s National Medical Research Council (NMRC/1208/2009 and NMRC/1247/2010) and Agency for Science, Technology and Research (A*STAR: SERC 1021290099), respectively. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.