Infection Control & Hospital Epidemiology
233
for extended periods of time. Surgical masks have been shown to provide inadequate protection against droplet nuclei with failure rates ranging from 10% to 90%.6 N95 respirators require certifi- cation by the National Institute for Occupational Safety and Health based on filter efficiencies with an assigned protection factor (APF) of 10.7 The APF indicates a reduction of aerosol concentration to one-tenth of the outside concentration, which equates to blocking 90% of biological hazards including viruses. Investigators have attempted to assess the protective impact of N95 respirators and surgical masks.3 Although respiratory pro- tection reduced respiratory infections, no definitive differences were detected between N95 respirators and surgical masks. We previously undertook a pilot study testing surgical masks
against N95 respirators using a human exposure model.4 With goggles, surgical masks failed to protect 3 of 4 participants. N95 respirators blocked influenza in 4 of 5 participants. Building upon these findings, we set out to assess the efficacy of N95 respirators. A novel half-mask PAPR was selected as a control providing an APF of at least 50 (ie, 98% biohazard blockage). Participants wearing N95 respirators encountered break-
Fig. 1. Exposure test chamber set-up.
and proportions, were calculated for the demographic data of the subjects. To estimate the exact 95% confidence interval (CI) around the proportion observed, the Clopper-Pearson method was used for calculation of that range. SAS version 9.4 software (SAS Institute, Cary, NC) was used for all analyses.
Results
In total, 58 participants were exposed to LAIV (mean age, 31 years; range, 21–49 years; male, 33%). Influenza virus was newly detected on the nasal swabs of 3 subjects after exposure wearing N95 respirators (10%; n=29; 95% confidence interval [CI], 0.02–0.27) (Fig. 1). Total RNA recovered from the 3 subjects were 4,745 copies, 5,471 copies, and 65,206 copies (mean, 25,141 copies). No virus was found in subjects wearing the PAPR (n=29; 95% CI, 0–0.12). The 3 subjects with virus detection included 2 white males (ages 31 and 40 years) and 1 black female (age 23 years).
Discussion
There has been considerable controversy regarding the infection control recommendations for influenza.5 Seasonal influenza is thought to be transmitted via droplets, defined as large, heavier particles compared to smaller aerosols (droplet nuclei ≤5 µm). The CDC recommends surgical masks to block large droplet transmission.1 N95 respirators should be worn during aerosol- generating procedures such as extubation and intubation, airway suction, and positive pressure ventilation, or when novel influenza strains are suspected. However, a growing body of evidence indicates that influenza,
seasonal or novel, is spread not only by large droplets but also via droplet nuclei able to travel long distances and remain airborne
through events to LAIV in 3 of 29 cases (10%), confirming our previous findings. This matches the 90% blocking of biohazards indicated by the APF of 10. The PAPR completely blocked transmission of LAIV. The findings represent the protective efficacy of the devices since wearers covered their eyes disrupting trans-ocular transmission.4 This study has several limitations.We used vaccine strains diluted in
saline solution to simulate exposure to influenza. Wild-type viruses naturally aerosolized by sneezing, coughing, or breathing may display different transmission characteristics. However, successful transmission was assessed directly after exposure, making it less likely to be influ- enced by the need for virus replication or signs of infectivity. RT-PCR is more sensitive than virus cell culture, but it does not provide proof of viability. Previous studies have correlated the amount of decay of influenza virus aerosols to RNA copies, establishing a ratio of 150–650 RNA copies to 1 tissue culture infectious dosage (TCID50).8 Given a human infectious dosage (HID50)of0.6–3 TCID50,anRNA load of 90–1,950 copies is necessary to infect an individual.9 In a previous study, all influenza emitters met the above threshold during routine care.10 RNA copies recovered from the respiratory tracts of the 3 participants ranged from 4,500 to >65,000, superseding the HID50 and making inoculation likely. Our knowledge regarding the efficacy of respiratory equipment
against virus transmission is mainly based on material testing and field studies in outbreak situations. Using a controlled human exposure model this study demonstrated successful blockage in 90% of influenza virus transmissions for N95 respirators with eye protection. However, a 10% failure rate compared to the complete protection provided by a PAPR raises the question of acceptable limits for virus exposure especially to resistant or novel pathogens.
Acknowledgments. None.
Financial support. The study was supported by a research grant from Celios (Tampa, FL).
Conflicts of interest. W.E.B. reports receiving grant support from Celios. All other authors do not have conflicts of interest.
References 1. Prevention strategies for seasonal influenza in healthcare settings. Centers for Disease Control and Prevention website.
http://www.cdc.gov/flu/
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156
