DHS Master Question List for COVID-19

The Department of Homeland Security (DHS) Science and Technology Directorate (S&T) developed the following “master question list” that quickly summarizes what is known, what additional information is needed, and who may be working to address such fundamental questions as, “What is the infectious dose?” and “How long does the virus persist in the environment?” The Master Question List (MQL) is intended to quickly present the current state of available information to government decision makers in the operational response to COVID-19 and allow structured and scientifically guided discussions across the federal government without burdening them with the need to review scientific reports, and to prevent duplication of efforts by highlighting and coordinating research.

Updated 7/7/2020

Table of Contents

Infectious Dose – How much agent will make a healthy individual ill? ..................................................................................... 3

The human infectious dose of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unknown by all exposure routes. SARS-CoV-2 is the cause of coronavirus disease 19 (COVID-19). Studies from other animal models are used as surrogates for humans.
Identifying the infectious dose for humans by the various routes through which we become infected is critical to the effective development of computational models to predict risk, develop diagnostics and countermeasures, and effective decontamination strategies. Animal studies are a plausible surrogate.

Transmissibility – How does it spread from one host to another? How easily is it spread? ...................................................... 4

SARS-CoV-2 is passed easily between humans, likely through close contact with relatively large droplets and possibly through smaller aerosolized particles.
Individuals can transmit SARS-CoV-2 to others before they have symptoms.
Undetected cases play a major role in transmission, and most cases are not reported.543

Individuals who have recovered clinically, but test positive, appear unable to transmit COVID-19.
The relative contribution of different routes of transmission, such as close contact and droplet transmission versus aerosol transmission and contaminated objects and surfaces (fomites), is unknown and requires additional research.

Host Range – How many species does it infect? Can it transfer from species to species? ......................................................... 5

SARS-CoV-2 is closely related to other coronaviruses circulating in bats in Southeast Asia. Previous coronaviruses have passed through an intermediate mammal host before infecting humans, but the identity of the SARS-CoV-2 intermediate host is unknown.
SARS-CoV-2 uses the same receptor for cell entry as the SARS-CoV-1 coronavirus that circulated in 2002/2003.

To date, ferrets, mink, hamsters, cats, and primates have been shown to be susceptible to SARS-CoV-2 infection. It is unknown whether these animals can transmit infection to humans.
Several animal models have been developed to recreate human-like illness, though to date they have been infected with high dose exposures. Lower dose studies may better replicate human disease acquisition.

Incubation Period – How long after infection do symptoms appear? Are people infectious during this time?.......................... 6

The majority of individuals develop symptoms within 14 days of exposure. For most people, it takes at least 2 days to develop symptoms, and on average symptoms develop 5 days after exposure. Incubating individuals can transmit disease for several days before symptom onset. Some individuals never develop symptoms but can still transmit disease.
The incubation period is well-characterized. Patients may be infectious, however, for days before symptoms develop.

Clinical Presentation – What are the signs and symptoms of an infected person? ................................................................... 7

Many COVID-19 cases are asymptomatic. Most symptomatic cases are mild, but severe disease can be found in any age group.3 Older individuals and those with underlying medical conditions are at higher risk of serious illness and death. The case fatality rate varies substantially by patient age and underlying comorbidities.
Additional studies on vulnerable subpopulations are required.

Children are susceptible to COVID-19,132 though generally show milder85, 303 or no symptoms.
The true case fatality rate is unknown, as the exact number of cases is uncertain. Testing priorities and case definitions vary by location. The proportion of asymptomatic infections is not known.

Protective Immunity – How long does the immune response provide protection from reinfection? ........................................ 8

Infected patients show productive immune responses, but the duration of any protection is unknown. Currently, there is no evidence that recovered patients can be reinfected with SARS-CoV-2.
As the pandemic continues, long-term monitoring of immune activity and reinfection status is needed.

Clinical Diagnosis – Are there tools to diagnose infected individuals? When during infection are they effective? .................... 9

Diagnosis relies on identifying the genetic signature of the virus in patient nose, throat, or sputum samples, or by identifying SARS-CoV-2 antibodies in individuals exposed to the virus. Confirmed cases are still underreported.
Validated serological (antibody) assays are being developed to help determine who has been exposed to SARS-CoV-2. Serological evidence of exposure does not indicate immunity.

CLEARED FOR PUBLIC RELEASE 1

REQUIRED INFORMATION FOR EFFECTIVE INFECTIOUS DISEASE OUTBREAK RESPONSE SARS-CoV-2 (COVID-19)

In general, PCR tests appear to be sensitive and specific, though confirmation of symptoms via chest CT is recommended. The sensitivity and specificity of serological testing methods is variable, and additional work needs to be done to determine factors that affect test accuracy.

Medical Treatments – Are there effective treatments?...........................................................................................................10

Treatment for COVID-19 is primarily supportive care,185, 320 and no single standard of care exists. Drug trials are ongoing. Remdesivir shows promise for reducing symptom duration in humans.33Hydroxychloroquine is associated with risk of cardiac arrhythmias and provides limited to no clinical benefit at this time. Dexamethasone may significantly reduce mortality in severely ill and ventilated patients.

Other pharmaceutical interventions are being investigated.

Additional information on treatment efficacy is required, particularly from large randomized clinical trials.

Vaccines – Are there effective vaccines?.................................................................................................................................11

Work is ongoing to develop a SARS-CoV-2 vaccine in human trials (e.g., Operation Warp Speed). Early results are being released, but evidence should be considered preliminary until larger trials are completed.
Published results from randomized clinical trials (Phase I – III) are needed.

Non-pharmaceutical Interventions – Are public health control measures effective at reducing spread?.................................12

Broad-scale control measures such as stay-at-home orders are effective at reducing movement and contact rates, and modeling shows evidence that they reduce transmission.
Research is needed to help plan for easing of restrictions.
As different US states have implemented differing control measures at various times, a comprehensive analysis of social distancing efficacy has not yet been conducted.

Environmental Stability – How long does the agent live in the environment?.........................................................................13

SARS-CoV-2 can persist on surfaces for at least 3 days and on the surface of a surgical mask for up to 7 days depending on conditions. If aerosolized intentionally, SARS-CoV-2 is stable for at least several hours. The seasonality of COVID-19 transmission is unknown. SARS-CoV-2 on surfaces is inactivated rapidly with sunlight.
Additional testing on SARS-CoV-2, as opposed to surrogate viruses, is needed to support initial estimates of stability. Tests quantifying infectivity, rather than the presence of viral RNA, are needed.

Decontamination – What are effective methods to kill the agent in the environment? ..........................................................14

Soap and water, as well as common alcohol and chlorine-based cleaners, hand sanitizers, and disinfectants are effective at inactivating SARS-CoV-2 on hands and surfaces.
Additional decontamination studies, particularly with regard to PPE and other items in short supply, are needed.

PPE – What PPE is effective, and who should be using it? .......................................................................................................15

The effectiveness of PPE for SARS-CoV-2 is currently unknown, and data from other related coronaviruses are used for guidance. Healthcare workers are at high risk of acquiring COVID-19, even with recommended PPE.
Most PPE recommendations have not been made on SARS-CoV-2 data, and comparative efficacy of different PPE for different tasks (e.g., intubation) is unknown. Identification of efficacious PPE for healthcare workers is critical due to their high rates of infection.

Forensics – Natural vs intentional use? Tests to be used for attribution. ................................................................................16

All current evidence supports the natural emergence of SARS-CoV-2 via a bat and possible intermediate mammal species. Identifying the intermediate species between bats and humans would aid in reducing potential spillover from a natural source. Wide sampling of bats, other wild animals, and humans is needed to address the origin of SARS-CoV-2.

Genomics – How does the disease agent compare to previous strains? ..................................................................................17

Current evidence suggests that SARS-CoV-2 accumulates substitutions and mutations at a similar rate as other coronaviruses. Mutations and deletions in specific portions of the SARS-CoV-2 genome have not been linked to any changes in transmission or disease severity, though modeling work is attempting to identify possible changes.
Research linking genetic changes to differences in phenotype (e.g., transmissibility, virulence, progression in patients) is needed.

Forecasting – What forecasting models and methods exist?...................................................................................................18

Forecasts differ in how they handle public health interventions such as shelter-in-place orders and tracking how methods change in the near future will be important for understanding limitations going forward.

reduce COVID transmission

VERDICT

• The 2-metre social distancing rule assumes that the dominant routes of transmission of SARS-CoV-2 are via respiratory large droplets falling on others or surfaces.

• A one-size-fits-all 2-metre social distancing rule is not consistent with the underlying science of exhalations and indoor air. Such rules are based on an over-simplistic picture of viral transfer, which assume a clear dichotomy between large droplets and small airborne droplets emitted in isolation without accounting for the exhaled air. The reality involves a continuum of droplet sizes and an important role of the exhaled air that carries them.

• Smaller airborne droplets laden with SARS-CoV-2 may spread up to 8 metres concentrated in exhaled air from infected individuals, even without background ventilation or airflow. Whilst there is limited direct evidence that live SARS-CoV-2 is significantly spread via this route, there is no direct evidence that it is not spread this way.

• The risk of SARS-CoV-2 transmission falls as physical distance between people increases, so relaxing the distancing rules, particularly for indoor settings, might therefore risk an increase in infection rates. In some settings, even 2 metres may be too close.

• Safe transmission mitigation measures depend on multiple factors related to both the individual and the environment, including viral load, duration of exposure, number of individuals, indoor versus outdoor settings, level of ventilation and whether face coverings are worn.

• Social distancing should be adapted and used alongside other strategies to reduce transmission, such as air hygiene, involving in part maximizing and adapting ventilation  to specific indoor spaces, effective hand washing, regular surface cleaning, face coverings where appropriate and prompt isolation of affected individuals.

…violent respiratory events’, e.g. coughing and sneezing, generate a warm, moist and turbulent gas cloud with forward momentum.

…Volume of speech may impact on droplet spread and subsequent risk of transmission, 

…Clusters of coronavirus have occurred during prolonged ‘violent exhalation events’ such as singing or fitness dance classes in confined locations.

… Viral shedding (higher with coughing/sneezing) and factors related to airflow in indoor environments, such as ventilation, may increase droplet spread.

… odds of transmission in an enclosed environment were 18.7-fold higher than in an outdoor environment.

…environmental factors are important in addition to physical distance in determining risk of transmission.

… Factors suggested include virus concentration in respiratory fluid, levels of pollution or particulate matter in the air, humidity, temperature, indoor versus outdoor environments, symptomatic versus asymptomatic hosts, and an individual’s baseline susceptibility to infection.

…virus is also stable in air for at least 3 hours, with others suggesting it may be stable for up to 16 hours.

…Many studies were of retrospective design, and hence at risk of recall bias in terms of distance to infected individual and selection bias in terms of identifying recent contacts, particularly those that relied on contact tracing alone. Confounding variables, such as disease severity, time since symptom onset and contact with other individuals, were rarely reported. 

Disclaimer: The article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. 

DARE to question things implemented with no evidence

A retrospective of the madness of crowds…

DARE Marks a Decade of Growth and Controversy

Today [Sep. 9, 1993], 5,200 communities in all 50 states have DARE programs, and more than 5.5 million children this year will learn about drugs through police officers using the DARE curriculum. At home, DARE has been called the first test of community-based policing, a law enforcement notion favored by Police Chief Willie L. Williams that involves bringing police officers into contact with the communities they patrol.

A brief history of DARE

DARE was founded in 1983 as a partnership between the Los Angeles Police Department and the L.A. public schools. The idea was simple: Officers would go into schools to talk to kids, “boosting the self-esteem of students so that they can resist the temptation to use drugs,” as the Los Angeles Times put it in a 10-year retrospective on the program in 1993.

The program drew bipartisan praise and spread like wildfire. Politicians realized that by supporting DARE, they could paint themselves as pro-cops and pro-kids: a win-win. President Ronald Reagan proclaimed the first “National DARE Day” in 1988, a tradition that continued well into the Obama administration.

Eventually, the program was in place in up to 75 percent of the nation’s school districts, by DARE’s own count. At its height, the group boasted an eight-figure budget, with much of that money coming from government sources. Individual state affiliates raised millions more.

But with success came scrutiny. Public health researchers started looking for evidence that the program was meeting its goals of reducing teen drug use. The first wave of studies, published in the early 1990s, didn’t find any.

Studies on effectiveness

1992 – Indiana University

Researchers at Indiana University, commissioned by Indiana school officials in 1992, found that those who completed the D.A.R.E. program subsequently had significantly higher rates of hallucinogenic drug use than those not exposed to the program.

1994 – RTI International

In 1994, three RTI International scientists evaluated eight previously-done quantitative analyses on DARE's efficacy that were found to meet their requirements for rigor. The researchers found that DARE's long-term effect couldn't be determined, because the corresponding studies were "compromised by severe control group attrition or contamination." However, the study concluded that in the short-term "DARE imparts a large amount of information, but has little or no impact on students' drug use," and that many smaller, interactive programs were more effective.

After the 1994 Research Triangle Institute study, an article in the Los Angeles Times stated that the "organization spent $41,000 to try to prevent widespread distribution of the RTI report and started legal action aimed at squelching the study." The director of publication of the American Journal of Public Health told USA Today that "D.A.R.E. has tried to interfere with the publication of this. They tried to intimidate us."

1995 – California Department of Education

In 1995, a report to the California Department of Education by Joel Brown Ph. D. stated that none of California's drug education programs worked, including D.A.R.E. "California's drug education programs, D.A.R.E. being the largest of them, simply doesn't work. More than 40 percent of the students told researchers they were 'not at all' influenced by drug educators or programs. Nearly 70 percent reported neutral to negative feelings about those delivering the antidrug message. While only 10 percent of elementary students responded to drug education negatively or indifferently, this figure grew to 33 percent of middle school students and topped 90 percent at the high school level." In some circles educators and administrators have admitted that DARE in fact potentially increased students exposure and knowledge of unknown drugs and controlled substances, resulting in experimentation and consumption of narcotics at a much younger age. Criticism focused on failure and misuse of tax-payer dollars, with either ineffective or negative result state-wide. 

1998 – National Institute of Justice

In 1998, a grant from the National Institute of Justice to the University of Maryland resulted in a report to the NIJ, which among other statements, concluded that "D.A.R.E. does not work to reduce substance use." D.A.R.E. expanded and modified the social competency development area of its curriculum in response to the report. Research by Dr. Dennis Rosenbaum in 1998 found that D.A.R.E. graduates were more likely than others to drink alcohol, smoke tobacco and use illegal drugs. Psychologist Dr. William Colson asserted in 1998 that D.A.R.E. increased drug awareness so that "as they get a little older, they (students) become very curious about these drugs they've learned about from police officers." The scientific research evidence in 1998 indicated that the officers were unsuccessful in preventing the increased awareness and curiosity from being translated into illegal use. The evidence suggested that, by exposing young impressionable children to drugs, the program was, in fact, encouraging and nurturing drug use. Studies funded by the National Institute of Justice in 1998, and the California Legislative Analyst's Office in 2000 also concluded that the program was ineffective.

1999 – Lynam et al.

A ten-year study was completed by the Donald R. Lynam and colleagues in 2006 involving one thousand D.A.R.E. graduates in an attempt to measure the effects of the program. After the ten-year period, no measurable effects were noted. The researchers compared levels of alcohol, cigarette, marijuana and the use of illegal substances before the D.A.R.E. program (when the students were in sixth grade) with the post D.A.R.E. levels (when they were 20 years old). Although there were some measured effects shortly after the program on the attitudes of the students towards drug use, these effects did not seem to carry on long term.

2001 – Office of the Surgeon General

In 2001, the Surgeon General of the United States, David Satcher M.D. Ph.D., placed the D.A.R.E. program in the category of "Ineffective Primary Prevention Programs". The U.S. General Accounting Office concluded in 2003 that the program was sometimes counterproductive in some populations, with those who graduated from D.A.R.E. later having higher than average rates of drug use (a boomerang effect).

2007 – Perspectives on Psychological Science

In March 2007, the D.A.R.E. program was placed on a list of treatments that have the potential to cause harm in clients in the APS journal, Perspectives on Psychological Science.

2008 – Harvard

Carol Weiss, Erin Murphy-Graham, Anthony Petrosino, and Allison G. Gandhi, "The Fairy Godmother—and Her Warts: Making the Dream of Evidence-Based Policy Come True," American Journal of Evaluation, Vol. 29 No.1, 29–47(2008) Evaluators sometimes wish for a Fairy Godmother who would make decision makers pay attention to evaluation findings when choosing programs to implement. The U.S. Department of Education came close to creating such a Fairy Godmother when it required school districts to choose drug abuse prevention programs only if their effectiveness was supported by "scientific" evidence. The experience showed advantages of such a procedure (e.g., reduction in support for D.A.R.E., which evaluation had found wanting) but also shortcomings (limited and in some cases questionable evaluation evidence in support of other programs). Federal procedures for identifying successful programs appeared biased. In addition, the Fairy Godmother discounted the professional judgment of local educators and did little to improve the fit of programs to local conditions. Nevertheless, giving evaluation more clout is a worthwhile way to increase the rationality of decision making. The authors recommend research on procedures used by other agencies to achieve similar aims.

2009 – Texas A&M

"The Social Construction of 'Evidence-Based' Drug Prevention Programs: A Reanalysis of Data from the Drug Abuse Resistance Education (DARE) Program," Evaluation Review, Vol. 33, No.4, 394–414 (2009). Studies by Dave Gorman and Carol Weiss argue that the D.A.R.E. program has been held to a higher standard than other youth drug prevention programs. Gorman writes, "what differentiates D.A.R.E. from many of the programs on evidence-based lists might not be the actual intervention but rather the manner in which data analysis is conducted, reported, and interpreted." Dennis M. Gorman and J. Charles Huber, Jr.

The U.S. Department of Education prohibits any of its funding to be used to support drug prevention programs that have not been able to demonstrate their effectiveness. Accordingly, D.A.R.E. America, in 2004, instituted a major revision of its curriculum which is currently being evaluated for possible effectiveness in reducing drug use.

The U.S. Substance Abuse and Mental Health Services Administration (SAMHSA) identified alternative start-up regional programs, none of which have longevity nor have they been subjected to intense scrutiny.

Project D.A.R.E. Outcome Effectiveness Revisited

Objectives. We provide an updated meta-analysis on the effectiveness of Project D.A.R.E. in preventing alcohol, tobacco, and illicit drug use among school-aged youths.

Methods. We used meta-analytic techniques to create an overall effect size for D.A.R.E. outcome evaluations reported in scientific journals.

Results. The overall weighted effect size for the included D.A.R.E. studies was extremely small (correlation coefficient = 0.011; Cohen d = 0.023; 95% confidence interval = −0.04, 0.08) and nonsignificant (z = 0.73, NS).

Conclusions. Our study supports previous findings indicating that D.A.R.E. is ineffective.

Analysis of HOV lanes

The United States has invested heavily in High Occupancy Vehicle (HOV) lanes despite very little evidence showing HOV lanes deliver on their promise to reduce vehicle miles traveled (VMT) and improve air quality.

Why indoor ventilation is important

…to reduce Covid-19 cases Building ventilation is always an important part of a healthy building environment as it ensures that a steady stream of outside air is brought into the building whilst stale air is exhausted. Stale air includes bioeffluents (body odours and exhaled breath), airborne pollutants (such as smells from cleaning products and furniture), amongst others. Ventilation is also a very important way of diluting any airborne pathogens and there is good evidence that demonstrates room occupants are more at risk of catching an illness in a poorly ventilated room than in a well-ventilated room. This is because in a poorly ventilated room occupants are exposed to a higher concentration of airborne pathogens, and the risk will increase with a greater amount of time spent in such an environment.

Risk = exposure x time

The risk of airborne infection to the individual can therefore be reduced by:

- Reducing time spent in the location

- Reducing airborne exposure concentration of infectious material

- Reducing risk of contact spread through regular handwashing, surface cleaning and reducing deposition of infectious particles.

Ventilation rate and effectiveness play a role in both airborne exposure and deposition rates. The risk for SARS-CoV2 transmission will be from asymptomatic or pre-symptomatic individuals who occupy a building without knowledge that they are shedding viral particles. Current government advice should be consulted with regards to reducing risks posed by symptomatic individuals. 1.1 Covid risks Evidence is beginning to emerge that SARS-CoV2, the virus which causes Covid-19, can spread by very small particles – called aerosols – which are released by an infected person when they cough, sneeze, talk and breathe, as well as the larger droplets that are released. Larger droplets will fall by gravity and influences the 2m social distancing measures to reduce spread. However, these fine aerosols can remain airborne for several hours. Although it can be difficult to definitively prove airborne transmission, our knowledge of other similar viruses and the emerging evidence showing high rates of infection in poorly ventilated rooms suggests that we should consider this as a potential transmission route and undertake measures to reduce that risk. These small droplets may be breathed in and cause infection. As our understanding of the significance of the various transmission routes of SARS-CoV2 develops, we recommend increasing the rate of supply of outside air to occupants wherever it is practical as a pre-cautionary measure. This is particularly important in poorly ventilated areas. Increasing the ventilation rate helps dilute any airborne contamination and reduces the risk of exposure for building users. This guidance is subject to change as SARS-CoV2 transmission routes become more clearly defined. Until then this takes a risk averse approach to reduce indoor pollution without significant capital expenditure

Which Mask And When? (Australian Dental)

Which mask?

Masks supplied for use in dental practice are required to conform to AS/NZS 4381 developed by Standards Australia. This standard specifies types of masks and their use. Below is an explanation of the types of masks that dental practitioners might use.

LEVEL 1 
Level 1 masks are not generally or widely used in dental practice, and they would only be appropriate where there is no risk of blood or body fluid splash. This may be the case in some areas of practice (e.g. when conducting post-insertion reviews for removable prosthodontics, mouthguards or removable orthodontic appliances, or performing orthodontic adjustments which exclude the use of the triplex syringe).  
 
LEVEL 2 
Level 2 masks are most commonly used in dental practices due to their ability to block particle sizes commonly encountered in routine dental practice. Restorative, endodontic and periodontal procedures using powered devices such as air turbine high-speed drills, ultrasonic scalers and triplex syringes generate large quantities of aerosols of three microns or less in size.

When undertaking such procedures, National Health and Medical Research Council (NHMRC) and ADA Infection Control Guidelines stipulate that clinical staff are to wear surgical masks which meet Standard AS 4381 that block particles of three microns or less in size, with level 2 splash resistance, so that splashes of fluid do not compromise the filtration performance of the mask.

A correctly fitted well-adapted Level 2 surgical mask will block 95% of total viral influenza particles, but effectiveness drops to 56% or less if loosely fitted or if the mask is gaping at its sides. Instructions available HERE.

LEVEL 3
Level 3 masks have a higher level of splash protection and are used for procedures where there is a greater risk for potential exposure to blood and body fluids, such as surgical procedures and major trauma. The correct use of Level 3 masks is specified in Australian Standard AS4381:2002.
 
During the COVID-19 pandemic Level 2 and 3 surgical masks may be used while treating low risk and medium risk cases (where aerosols are avoided).

P2/N95 Respirators

Airborne precautions are required when treating medium risk COVID-19 patients if aerosol generation is likely (there is no reasonable alternative), and for all treatment of high-risk patients. Airborne precautions, such as wearing P2 (N95) surgical respirators, are designed to reduce the likelihood of transmission of microorganisms that remain infectious over time and distance when suspended in the air. In addition to COVD-19, other infectious agents for which airborne precautions are indicated include measles, chickenpox (varicella), and Mycobacterium tuberculosis, as well as novel respiratory pathogens such as H5N1 influenza and avian influenza.

Maintaining safe practice

With respect to the challenges many practices are facing as a consequence of the mask supply issue it is vital that as a profession and individuals maintain safe practices, to protect ourselves, our staff, our patients, family and friends.

Examples of unacceptable practices include:

• Using one mask for more than one patient.

• Using one mask for more than 2 hours.

• Resterilising masks. Steam sterilising would alter the charge on the microfibers that are responsible for particle filtration, cause degradation of the mask straps, render the splash protection useless, and cause parts of the mask to disintegrate or melt, and release some toxic vapours.

• Using a cloth (e.g. cotton or gauze) mask.  These have poor filtration (no bacterial filtration or particle filtration), no splash protection and no resistance to fluids from the user coming through.

• Using a face-shield with no mask.

Similarly, it is important that we all be prudent in our use of masks as a consumable item as overuse will contribute to a greater supply issue. For example, it is not necessary for a dental assistant to change their mask at the end of a patient appointment just to undertake the normal change-over environmental cleaning stage.

ADA Guidelines for Infection Control

Page 8 of the ADA's Infection Control Guidelines offers further information as outlined below:

Dental procedures can generate large quantities of aerosols of three microns or less in size and a number of diseases may be transmitted via the airborne (inhalational) route. In the dental surgery environment, the most common causes of airborne aerosols are the high-speed air rotor handpiece, the ultrasonic scaler and the triplex syringe. The aerosols produced may be contaminated with bacteria and fungi from the oral cavity (from saliva and dental biofilms), as well as viruses from the patient’s blood. Therefore, dental practitioners and clinical support staff must wear suitable fluid-resistant surgical masks that block particles of three microns or less in size.

Masks protect the mucous membranes of the nose and mouth and must be worn wherever there is a potential for splashing, splattering or spraying of blood, saliva or body substances, or where there is a probability of the inhalation of aerosols with a potential for transmission of airborne pathogens. However, it is suggested that masks be worn at all times when treating patients to prevent contamination of the working area with the operator’s respiratory or nasal secretions/organisms.

Surgical masks for dental use are fluid-repellent paper filter masks and are suitable for both surgical and non-surgical dental procedures that generate aerosols. The filtration abilities of a mask begin to decline with moisture on the inner and outer surfaces of the mask after approximately 20 minutes. It is difficult to change masks during long procedures (such as surgical procedures) and is not necessary unless the mask becomes completely wet from within or without.