Facemask Use by Children During Infectious Disease Outbreaks

Abstract

An overview of available literature on the use of protective facemasks by children for protection from respiratory infectious agents reveals relatively few articles dealing specifically with the topic, despite their use during recent outbreaks (eg, severe acute respiratory syndrome, pandemic influenza). Little is known about the physiological and psychological burdens imposed by these devices and a child's ability to correctly use and tolerate them. This article focuses on the myriad issues associated with protective facemask use by children in the hope of educating public health personnel, healthcare professionals, and families on their limitations and associated risks, and in the hope of fostering much-needed research.

Little is known about the physiological and psychological effects of facemasks when worn by children. Facemasks have been used during recent infectious disease outbreaks to protect children from respiratory infectious agents, but we need to know more about a child's ability to correctly use and tolerate them.

Recent experience with serious viral respiratory pathogen outbreaks (eg, pandemic influenza [H1N1], severe acute respiratory syndrome [SARS], avian influenza [H5N1]) has highlighted the need for respiratory protection as one measure to prevent exposure to and limit dissemination of disease. Several studies have demonstrated that the use of protective facemasks (PFMs) is associated with decreased transmission of infectious agents.^1–3 (For the purposes of this article, PFMs will include surgical/medical facemasks [SMs] and filtering facepiece respirators [FFRs].) Although a significant body of scientific data exists on the use and effects of these devices in adults, there is relatively sparse data on their use by children, despite the fact that children under 18 years of age account for a quarter of the U.S. population and that young children are more vulnerable to influenza and its complications than are adolescents and adults.⁴ Recent respiratory pathogen outbreaks, which disproportionately affected children and young adults,^5,6 serve to underscore the need for investigation in this area.

Despite the relative lack of scientific evidence on the physiological and psychological impact of PFM wear by children, there have been calls by researchers, medical personnel, and public health authorities for the widespread use of these devices by children, including toddlers.^7,8 At the same time, medical professional societies have called on federal agencies to conduct research regarding their use by children.^9,10 Meanwhile, manufacturers are actively promoting the sale of child-size protective facemasks,^11,12 and, despite the lack of concrete evidence to support widespread use by the general public, a permissive approach to the use of PFMs has been recommended in many countries.¹³

A computerized literature search was undertaken for the period 1950 to 2010 with the search engines Medline, OvidSP, EMBase, PsycINFO, Compendex, and Google, using the search terms “respiratory protective equipment,” “facemasks,” “protective facemasks,” “filtering facepiece respirators,” “gas masks,” “children,” “complications,” and “pediatric facemask use.” Bibliographies of selected articles also were searched for relevant articles. A web-based search of relevant electronic references was performed using the aforementioned search terms, and selected textbook articles were referenced. Articles selected for inclusion in the review were those that included information relating to the use of protective facemasks by children, articles relating to the respiratory physiology of children, and references from government agencies involved in the guidance and investigation of respiratory protective equipment.

A total of 187 articles from the medical literature were retrieved along with 42 web-based articles and 1 textbook chapter cited in 1 of the aforementioned retrieved articles. Of the 229 total articles retrieved, only 68 directly or indirectly addressed the topic and thus serve as the database for this study. These included 52 articles published in peer-reviewed journals; 15 electronic references from medical, government, and news agency sources; and 1 textbook chapter. There is sparse published scientific data specifically addressing the issue of the use of protective facemasks in children.

Facemask Use

A child's respiratory system is not merely a miniaturization of an adult's; significant differences exist that can be affected by the use of protective facemasks. Filtering facepiece respirators, of which the N95 FFR model is the most commonly used, are tight-fitting disposable particulate respirators with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium that covers at least the mouth and nose and filters out harmful particles.¹⁴

Surgical/medical facemasks are loose-fitting disposable masks that cover the nose and mouth and are referred to by various names, such as surgical mask, medical mask, procedure mask, dental mask, laser mask, and homemade masks. SMs were initially introduced to prevent surgical personnel from contaminating the surgical field with respiratory droplets expelled during speaking, coughing, and sneezing, but also protect the wearer from splashes or sprays.⁹ Currently, SMs are recommended as source controls to be placed (when tolerable) on symptomatic patients to limit the spread of infectious respiratory secretions to others.¹⁴ Because of the loose fit of surgical/medical facemasks compared with filtering facepiece respirators, during inhalation much of the potentially contaminated air passes through gaps between the face and the SM so that these masks do not provide a high degree of protection from airborne particulates of small dimensions (ie, droplet nuclei) that might harbor pathogens.¹⁴ The variability in the protective qualities of surgical/medical facemasks compared with filtering facepiece respirators is highlighted by studies using inert and bio-aerosol challenges showing that SMs achieve filtration efficiencies of 0% to 99% (median 40%) compared with 95% to 99.5% for N95 FFRs.¹⁵ Issues of importance when addressing the use of protective facemasks by children include their effects on respiratory physiology, efficacy, facial anthropometrics, tolerance, safety, and regulatory issues.

Impact of Protective Facemasks on Respiratory Physiology

Dead Space

Respiratory dead space (V_D) is classically divided into 3 separate components: anatomic, apparatus, and alveolar.¹⁶ The total anatomic V_D of the respiratory tract for older children and adults is reported to be 2.2 ml/kg.¹⁷ Children have an anatomic V_D/tidal volume (V_T) ratio similar to that of adults (∼0.3).^17,18 However, the functional dead space that includes the PFM V_D (often expressed as the V_D/V_T ratio) has important implications when dealing with young children, where the contribution of the PFM V_D can represent a large fraction of a naturally small V_T.¹³ Although the effect of PFMs on children's V_D/V_T ratio is not precisely known, it has been shown that small-size anesthesia masks used during spontaneous ventilation increase the physiological dead space by upwards of 40% of V_T.¹⁹ Because V_D ventilation does not contribute to gas exchange, increases in V_D brought about through the use of PFMs could have a more profound effect on a child's ventilation than that of an adult. The effect on V_D is likely to be greater with a properly sized and fitted FFR than with an SM, because the tighter fit of the FFR more efficiently prevents the escape of gases that would decrease the static V_D.

Tidal Volume

Adults and children display approximately the same resting V_T (7-8 ml/kg) on a per-kilogram basis.^20,21 Although children do not breathe as deeply as adults, alveolar ventilation is sufficient for gas exchange because children's physiologic V_D is smaller than that of adults.²² Infants' and young children's ribs lie horizontally, so that the thoracic cage can only enlarge slightly by rib movement, necessitating maintenance of respiration chiefly by diaphragmatic movement that limits V_T and requiring an increase in the breathing rate to meet increased respiratory demands.²³ The additional V_D imposed by use of protective facemasks can result in an increase in the V_T, respiratory rate (f_B), or both.

Recent data have demonstrated nonsignificant increases in V_T associated with the use of filtering facepiece respirators at low work rates in adults²⁴ that may be at least partially related to the increased dead space of the FFR, but similar data on children are lacking. This effect could be more pronounced in children if the V_D/V_T ratio was increased significantly.¹⁶ Certain styles of protective facemasks (eg, duckbill and cup-shaped) have larger associated PFM V_D and would likely have a greater impact on the V_D/V_T ratio.

Deeper breathing has been reported in children undergoing pulmonary function testing with the use of a tight-fitting mask that had a static dead space of 133 ml,²⁵ which is approximately half the static dead space of a standard size adult FFR and would result in an elevated V_D/V_T ratio in a child. The effect of longer periods of PFM wear by children on the depth of breathing is unknown, but an increase in a child's depth of breathing will increase the work of breathing (energy expenditure), because it is less energy efficient.²⁶ Of further concern is the production of fast, variable heart rates in young children who breathe deeply for sustained periods.²⁷

Respiratory Rate

Children display an increased respiratory rate (f_B) compared to adults based on a higher resting metabolic rate and oxygen (O₂) consumption per unit body weight related to a larger surface area per unit body weight and the basal energy requirements for growth.^20,27 A child's higher baseline f_B is, from a physiological standpoint, more energy efficient than an increase in the depth of breathing because of differences in lung and rib compliances compared with adults.²⁰ Initially, the use of protective facemasks usually results in an increase in the f_B, which can be attributed to such factors as lack of acclimatization, increases in breathing resistance, physical discomfort (eg, facial pressure, facial heat, skin irritation, etc), psychogenic factors (eg, anxiety, claustrophobia), or sensory stimuli arising from the face, mouth, and nose.^28,29 Further, the addition of the PFM V_D increases the child's functional V_D, the impact of which is overcome through an increase in the f_B and minute volume,³⁰ because young children have a limited ability to increase pulmonary functional residual capacity and therefore increase their minute ventilation primarily by breathing faster rather than taking deeper breaths.²⁰

The use of filtering facepiece respirators, surgical/medical facemasks, and homemade (teacloth) masks by children during low energy expenditure tasks has been reported to elevate the f_B.³¹ Similarly, use of a tight-fitting facemask for pulmonary testing purposes has also been shown to result in an increased f_B in children;^25,32 however, this response can be attenuated in the majority of children by familiarization (eg, allowing the child to play with the mask prior to use).³² Also, children who have previously used PFM-like devices (eg, aerosolized bronchodilators via a mask) may adapt to use of PFM more readily because they are familiar with mask use and may not be frightened by it.²⁵ The impact on a child's f_B would generally be greater with an FFR than a flat or pleated SM because the latter offer less breathing resistance and create a smaller V_D since they fit more closely to the face than most FFR models (this would not necessarily hold true for duckbill and cup-shaped SMs).

Breathing Resistance

Breathing resistance (R_AW), the opposition to the flow of air through the respiratory passages (ie, nose, trachea, bronchi), affects the work of breathing, and approximately 65% of a child's R_AW is nasal.³³ Because a tight-fitting protective facemask such as a filtering facepiece respirator is associated with nasal breathing in children,³⁴ as opposed to mouth breathing induced by PFM wear in adults,³⁵ the R_AW while wearing an FFR could be increased and augment the work of breathing.

The breathing resistances of modern FFRs are relatively low and generally well below the National Institute for Occupational Safety and Health (NIOSH) FFR certification limits (ie, 35-mm and 25-mm H₂O pressure for inhalation and exhalation, respectively, at a constant airflow of 85 liters per minute using a breathing mannequin as a human surrogate) because of their relative thinness, due to improved filter materials and the incorporation of electrostatic charges for particle capture.³⁶ The tolerance of children to these breathing resistance limits is unknown. Surgical/medical facemasks display lower breathing resistance than FFRs because of comparatively decreased density. For example, the decrease in air flow pressure as air flows through a low resistance (ie, Type II) SM (at 8 liters per minute continuous airflow) is ≤3-mm H₂O pressure.³⁶ The inability to form a tight seal at the SM/face interface allows egress and ingress of some air from the sides of the mask and therefore partially bypasses the resistance of the filter material. Thus, from the limited data, it would appear that the low breathing resistance of SMs would be tolerable for children, but scientific validation of this presumption is lacking.

Oxygen saturation (SaO₂) is determined by the alveolar ventilation (amount of O₂ exchanged across alveolar membranes). The PFM V_D forms a partial repository for exhaled respiratory gases (O₂, nitrogen, carbon dioxide), a portion of which is re-entrained on successive inhalations.³⁷ Depending on the V_D/V_T ratio, increasing levels of carbon dioxide will result in decreased alveolar transport of O₂ according to the alveolar gas equation.²⁰ Recent work has shown that O₂ concentrations were lower within the V_D of FFRs, but did not affect SaO₂ over the course of 1 hour of low-level exercise.^24,38 Wearing an SM as an outer barrier over an FFR did not significantly affect SaO₂ compared to wearing an FFR alone,³⁷ suggesting that SMs had minimal clinical impact on SaO₂. Although no similar data are available for children, it seems likely that SMs, by virtue of their loose fit and low breathing resistance, would have minimal impact on a child's SaO₂. Nonetheless, minor decrements in SaO₂ associated with the use of SM by healthcare workers have recently been reported.³⁹

Carbon Dioxide

Normal carbon dioxide (CO₂) levels for children are 32-48 mm Hg. Increased levels of CO₂ are the major stimulus to an increase in ventilation at rest and during mild-to-moderate exercise, being manifested as increased f_B or V_T, or a combination of both. The ventilatory response to increased levels of CO₂ is generally similar in children and infants to adults.^40,41 Recent work has demonstrated that adults wearing FFRs and elastomeric air-purifying respirators over a 1-hour period at a low work rate had respirator V_D CO₂ levels in excess of Occupational Health and Safety Administration (OSHA) ambient workplace standards (ie, <0.5% CO₂), and some experienced mild-to-moderate elevations in transcutaneous CO₂ levels.^24,38,42 Wearing a surgical/medical facemask as an outer barrier over a filtering facepiece respirator did not significantly affect transcutaneous CO₂ levels, compared with wearing only an FFR, implying that SMs had little impact on CO₂ retention.³⁷ Although no data on the effect of CO₂ retention in children wearing FFRs or SMs are available, young children exercising on a treadmill at a moderate work rate while wearing a specially designed hooded respiratory protective device with an active air supply averaged only mildly elevated mean inspiratory CO₂ levels (0.7%,±0.6%) that did not exceed 1.6% in any individual,⁴⁰ whereas an elevated fraction of inspired CO₂ (>2%) was noted in 12 of 24 children (ages 3-8 years) using a gas mask/attached hood combination.⁴³

Efficacy

Filtering facepiece respirators may thwart the dispersal of airborne pathogens by blocking the rapid turbulent jet that is formed during coughing or sneezing, whereas surgical/medical facemasks redirect the turbulent jet laterally and posteriorly.⁴⁴ Children's greater social interactions make them a significant source of disease transmission, and it has been suggested that their use of SMs could have a significant impact on disease spread.⁷ One recent study determined that significant protection against airborne pathogens was shown to be afforded to children by protective facemasks in spite of imperfect fit, with SMs and FFRs offering fit factors (ratio of ambient particles to within-PFM particles) ranging from 1.9-99 for children, although these were significantly less than for adults.³¹ SMs and FFRs may help protect against some pathogens by preventing dissemination of the infected wearer's oral/nasal particulates generated by talking, coughing, or sneezing, or they may protect noninfected individuals in close proximity to expelled particulates.⁴⁵ SMs and FFRs can also prevent auto-innoculation occurring by touching the mouth, nose, or eyes with hands that harbor pathogens.⁴⁶

Facial Anthropometrics

Filtering facepiece respirators, as currently configured, are designed to fit adults, and it is doubtful that they would afford equivalent protection to children.⁹ Children's facial dimensions change throughout childhood development so that the fit (facial seal) of FFRs continually evolves and is difficult to predict, thus making it anthropometrically difficult to fit children with protective facemasks that depend on a tight seal. ⁴⁷ The fit of FFRs is very important because it is the major contributor of leakage into the wearer's breathing zone. Although FFRs in adult small-size categories may outwardly appear to fit older children, they are not designed to form a tight fit on the small faces of children, and protection is thereby compromised.^9,31,46 This is not surprising, since, like children, adults with small facial features also often have difficulty with passing respirator fit tests on various models of small-size FFRs.^48,49 SMs are loose-fitting PFMs that do not depend on a snug fit to ensure their primary functions of splash protection from body fluids and barrier protection from the wearer's exhaled particulates, but they offer less protection from small airborne particles (droplet nuclei) that may harbor pathogens.³¹ SMs are also more readily available in children's sizes than FFRs.

Tolerance to Wearing Protective Facemasks

Like adults, children's tolerance of protective facemasks can be affected negatively by any of a number of psychophysical factors, including, but not limited to, breathing resistance, heat and moisture buildup, CO₂ retention, facial pressure, claustrophobia, and anxiety.^43,50 In addition, children are affected by boredom and the lack of motivation to tolerate PFMs.^43,50,51

Although there is a general perception that children will not wear PFMs for protracted periods of time, there is some evidence to the contrary because children can be encouraged to wear PFMs through persuasion (eg, parental, societal, etc), education, incentives, and habituation.^25,32,49,51 For example, during the Gulf War, Israeli children wore gas masks (much greater breathing resistance than FFRs or SMs) for periods of up to 1 hour during missile attacks,^43,52 and, experimentally, children 7 to 10 years of age have tolerated gas masks and FFRs for upwards of 6 hours of continuous wear.⁵¹ In Asia, where it is considered a civic duty to wear appropriate protective facemasks, SARS-era schoolchildren routinely wore SMs throughout the academic day, including during examinations of verbal skills.^53,54 Pediatric patients wore SMs or FFRs continuously during inpatient care in a Toronto hospital during the SARS outbreaks,⁵⁵ and, in a study of the psychological response to PFM wear, ∼50% of children ages 7 to 10 years tolerated FFRs continuously for 6 hours of wear.⁵⁰ In one experimental study, 59% of grade school children tolerated daily wear of SMs over the course of the school day (except lunch and recess) for 1 week.⁵⁶ During the recent H1N1 pandemic, children were observed wearing SMs for extended periods in various venues (eg, school, during play activities, in crowded areas, etc),⁷ suggesting that they were tolerable to some degree. Asthmatic children have been shown to tolerate SMs during treadmill exercising and to benefit from the associated retention of warm humidified air.⁵⁷ SMs can generally be worn comfortably for longer periods of time than FFRs, because they are less dense and looser fitting.⁴⁶

Safety Issues

The unsupervised use of protective facemasks by children is not without risk, especially in very young children. During the Gulf War, several childhood deaths due to asphyxia, aspiration, or hypoxia were attributed to the use of PFMs and other respiratory protective devices (ie, gas masks, infant portable plastic carriers).⁵² The risk of pathogen dissemination or auto-innoculation from the outer surface of PFMs by the wandering and inquisitive fingers of children⁷ is also of concern, as is pathogen dispersal during improper doffing of PFMs, suggesting that their proper handling and disposal may be an unreasonable expectation for young children⁹ unless they are closely monitored. Further, reliance solely on SMs for protection against airborne pathogens, without consideration of other preventive measures, will be ineffective.⁵⁸ Children have difficulty communicating in various forms of PFMs and may not be able to readily notify others when they are having difficulties related to their wear.^50,51

Regulatory Issues

The U.S. Food and Drug Administration (FDA) clears medical devices but has not cleared surgical/medical facemasks designed for use by children.⁹ Nonetheless, recently CDC suggested their use in febrile, symptomatic children presenting to healthcare facilities, physician offices, and in crowded venues.⁵⁹ NIOSH, the federal agency that tests and certifies respiratory protective devices, has not certified filtering facepiece respirators for use by children and recommends that children should not do any work that requires wearing a respirator because of issues of fit and protection.⁶⁰

Nonetheless, some worksites (eg, family farms, orchards, etc) that use child labor are subject to respiratory protection requirements for their workers. However, various state and federal statutes may exempt children from certain portions of the requirements. For example, the Code of Federal Regulations' Hazardous Occupations Orders for Agriculture, which specifies 11 domains of work prohibited to children, exempts children who work on their parents' farms.⁶¹ Also, the state of Maine allows children who are 16 or 17 years old to perform emergency care (for which they are licensed) in an emergency vehicle that may require use of PFMs.⁶² Voluntary use of PFMs in workplaces, such as their use by children who perform volunteer services (eg, transporting residents in nursing home facilities), are not subject to OSHA regulations.

Conclusion

There is currently an ongoing debate as to the relative efficacy of surgical/medical facemasks versus filtering facepiece respirators in the control of airborne pathogen transmission,^63–65 but both types of protective facemasks have shown some efficacy in attenuating the dispersal of infectious agents by adults and children.^1,2 Unfortunately, there are very limited data on the imposed physiological and psychological burden, tolerance, and proper use of PFMs by children. Studies on the physiological impact of PFMs on adult users have shown that SMs offer little in the way of significant breathing resistance³⁸ or clinically significant impact on SaO₂ saturation parameters,^37,39 suggesting that SMs may also have less physiological impact on children compared with FFRs. However, SMs offer less protection than FFRs from airborne pathogens carried on droplet nuclei. FFRs are not currently certified by NIOSH nor are SMs cleared by the FDA for use by children; however, CDC and school district guidelines have suggested that the use of SMs by children is indicated in certain scenarios to prevent disease transmission.^58,66,67 Although these guidelines are based on the commonsense notion that SMs offer some (limited) protection against airborne pathogens, they are not fully grounded in scientific data,⁶⁸ and this disconnect between guidelines and available data highlights the critical need for research on the topic of PFM use by children.

Future research should address such issues as the relative merits of manufacturers' development of child-sized FFRs versus a greater focus on SMs for children; the applicability of current adult fitting, doffing, and donning instructions for training children in achieving adequate PFM fit; and the level of respiratory protection for children that is optimal in pandemic influenza situations that may arise in the future. Physiological and psychological research also is needed to clarify the physical and emotional impact of the wearing of protective facemasks on children.

Footnotes

Acknowledgments

The author thanks Roland BerryAnn and Drs. Ronald Shaffer, W. Jon Williams, and Ziqing Zhuang of the National Personal Protective Technology Laboratory/National Institute for Occupational Safety and Health, and Dr. Andrew Levinson and John Steelnack of the Office of Biological Hazards, Occupational Safety and Health Administration, for their manuscript reviews and helpful suggestions.

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