FAQ: What is the evidence on influenza and other virus aerosols and how this informs safety in patient care environments?

What is the evidence on influenza and other virus aerosols and how this informs safety in patient care environments – both in terms of HCP exposure and safety while providing care, and patient exposure from HCP and other workers in the patient care environment?  [FAQ Date: April 1, 2013]
Linked to evidence issues around masking is the technical evidence available about what the measurable exposures may be for both HCP and patients. The current literature below provides perspectives but are not prescriptive.


Exposure to Influenza Virus Aerosols During Routine Patient Care
Werner E. Bischoff, Katrina Swett, Iris Leng, and Timothy R. Peters
Journal of Infectious Diseases
Volume 207 Issue 7   April 1, 2013
J Infect Dis. (2013) 207(7): 1037-1046 doi:10.1093/infdis/jis773
Background. Defining dispersal of influenza virus via aerosol is essential for the  development of prevention measures.

Methods. During the 2010–2011 influenza season, subjects with influenza-like illness were enrolled in an emergency department and throughout a tertiary care hospital, nasopharyngeal swab specimens were obtained, and symptom severity, treatment, and medical history were recorded. Quantitative impaction air samples were taken not ≤0.305 m (1 foot), 0.914 m (3 feet), and 1.829 m (6 feet) from the patient’s head during routine care. Influenza virus was detected by rapid test and polymerase chain reaction.

Results. Sixty-one of 94 subjects (65%) tested positive for influenza virus. Twenty-six patients (43%) released influenza virus into room air, with 5 (19%) emitting up to 32 times more virus than others. Emitters surpassed the airborne 50% human infectious dose of influenza virus at all sample locations. Healthcare professionals (HCPs) were exposed to mainly small influenza virus particles (diameter, <4.7 µm), with concentrations decreasing with increasing distance from the patient’s head (P < .05). Influenza virus release was associated with high viral loads in nasopharyngeal samples (shedding), coughing, and sneezing (P < .05). Patients who reported severe illness and major interference with daily life also emitted more influenza virus (P < .05).

Conclusions. HCPs within 1.829 m of patients with influenza could be exposed to infectious doses of influenza virus, primarily in small-particle aerosols. This finding questions the current paradigm of localized droplet transmission during non–aerosol-generating procedures.

Influenza Virus Aerosols in Human Exhaled Breath: Particle Size, Culturability, and Effect of Surgical Masks
Donald K. Milton, M. Patricia Fabian, Benjamin J. Cowling, Michael L. Grantham, James J. McDevitt
PLoS One
Research Article | published 07 Mar 2013 | PLOS Pathogens 10.1371/journal.ppat.1003205
The CDC recommends that healthcare settings provide influenza patients with facemasks as a means of reducing transmission to staff and other patients, and a recent report suggested that surgical masks can capture influenza virus in large droplet spray. However, there is minimal data on influenza virus aerosol shedding, the infectiousness of exhaled aerosols, and none on the impact of facemasks on viral aerosol shedding from patients with seasonal influenza.

We collected samples of exhaled particles (one with and one without a facemask) in two size fractions (“coarse”>5 µm, “fine”≤5 µm) from 37 volunteers within 5 days of seasonal influenza onset, measured viral copy number using quantitative RT-PCR, and tested the fine-particle fraction for culturable virus.

Fine particles contained 8.8 (95% CI 4.1 to 19) fold more viral copies than did coarse particles. Surgical masks reduced viral copy numbers in the fine fraction by 2.8 fold (95% CI 1.5 to 5.2) and in the coarse fraction by 25 fold (95% CI 3.5 to 180). Overall, masks produced a 3.4 fold (95% CI 1.8 to 6.3) reduction in viral aerosol shedding. Correlations between nasopharyngeal swab and the aerosol fraction copy numbers were weak (r = 0.17, coarse; r = 0.29, fine fraction). Copy numbers in exhaled breath declined rapidly with day after onset of illness. Two subjects with the highest copy numbers gave culture positive fine particle samples.

Surgical masks worn by patients reduce aerosols shedding of virus. The abundance of viral copies in fine particle aerosols and evidence for their infectiousness suggests an important role in seasonal influenza transmission. Monitoring exhaled virus aerosols will be important for validation of experimental transmission studies in humans.

Author Summary
The relative importance of direct and indirect contact, large droplet spray, and aerosols as modes of influenza transmission is not known but is important in devising effective interventions. Surgical facemasks worn by patients are recommended by the CDC as a means of reducing the spread of influenza in healthcare facilities. We sought to determine the total number of viral RNA copies present in exhaled breath and cough aerosols, whether the RNA copies in fine particle aerosols represent infectious virus, and whether surgical facemasks reduce the amount of virus shed into aerosols by people infected with seasonal influenza viruses. We found that total viral copies detected by molecular methods were 8.8 times more numerous in fine (≤5 µm) than in coarse (>5 µm) aerosol particles and that the fine particles from cases with the highest total number of viral RNA copies contained infectious virus. Surgical masks reduced the overall number of RNA copies by 3.4 fold. These results suggest an important role for aerosols in transmission of influenza virus and that surgical facemasks worn by infected persons are potentially an effective means of limiting the spread of influenza.

Hand contamination during routine care in medical wards: the role of hand hygiene compliance
Olga Monistrol, M. Liboria López, Montserrat Riera, Roser Font, Carme Nicolás, Miguel Angel Escobar, Núria Freixas, Javier Garau, and Esther Calbo
Journal of Medical Microbiology
April 2013 62:623-629; published ahead of print January 17, 2013
Clinical microbiology and virology
J Med Microbiol doi:10.1099/jmm.0.050328-0
The hands of healthcare workers (HCWs) are the most common vehicle for the transmission of micro-organisms from patient to patient and within the healthcare environment. The aim of this study was to evaluate the impact of a multimodal campaign on the type and amount of resident and transient flora and the presence of potential risk factors for hand contamination during routine care. A before–after (PRE and POST periods) interventional study was carried out in medical wards of a tertiary care hospital. Eighty-nine samples were analysed. Samples were cultured immediately before patient contact using a glove-juice method. Data collected included socio-demographic and risk factors for hand contamination. Flora was measured as log10 c.f.u. ml−1 and evaluated by comparing median values in the PRE and POST periods. Transient flora was isolated from the hands of 67.4 and 46.1 % of HCWs in the PRE and POST periods, respectively (P<0.001). Enterobacteriaceae, Pseudomonas spp. and meticillin-sensitive Staphylococcus aureus were the predominant contaminants. Resident flora was isolated from 92.1 % of HCWs in the PRE period and from 70.8 % in the POST period (P<0.001). The meticillin-resistant coagulase-negative staphylococci log10 c.f.u. count ml−1 decreased from 1.96±1.2 to 0.89±1.2 (mean±sd; P<0.001), and the global flora count decreased from 2.77±1.1 to 1.56±1.4 (P<0.001). In the POST period, the wearing of fewer rings (P<0.001), shorter fingernail length (P = 0.008), a shorter time since recent hand hygiene (HH) (P = 0.007) and an increased use of alcohol-based hand rub instead of soap (P<0.001) were documented.   The HH multimodal strategy reduced the number of risk factors and the level of HCW hand contamination.

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