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REVIEW ARTICLE OPEN
Transmission routes of 2019-nCoV and controls
in dental practice
Xian Peng
1
, Xin Xu
1
, Yuqing Li
1
, Lei Cheng
1
, Xuedong Zhou
1
and Biao Ren
1
A novel β-coronavirus (2019-nCoV) caused severe and even fetal pneumonia explored in a seafood market of Wuhan city, Hubei
province, China, and rapidly spread to other provinces of China and other countries. The 2019-nCoV was different from SARS-CoV,
but shared the same host receptor the human angiotensin-converting enzyme 2 (ACE2). The natural host of 2019-nCoV may be the
bat Rhinolophus affinis as 2019-nCoV showed 96.2% of whole-genome identity to BatCoV RaTG13. The person-to-person
transmission routes of 2019-nCoV included direct transmission, such as cough, sneeze, droplet inhalation transmission, and contact
transmission, such as the contact with oral, nasal, and eye mucous membranes. 2019-nCoV can also be transmitted through the
saliva, and the fetal–oral routes may also be a potential person-to-person transmission route. The participants in dental practice
expose to tremendous risk of 2019-nCoV infection due to the face-to-face communication and the exposure to saliva, blood, and
other body fluids, and the handling of sharp instruments. Dental professionals play great roles in preventing the transmission of
2019-nCoV. Here we recommend the infection control measures during dental practice to block the person-to-person transmission
routes in dental clinics and hospitals.
International Journal of Oral Science (2020) 12:9 ; https://doi.org/10.1038/s41368-020-0075-9
INTRODUCTION
An emergent pneumonia outbreak originated in Wuhan City, in
the late December 2019
1
. The pneumonia infection has rapidly
spread from Wuhan to most other provinces and other 24
countries
2,3
. World Health Organization declared a public health
emergency of international concern over this global pneumonia
outbreak on 30th January 2020.
The typical clinical symptoms of the patients who suffered from
the novel viral pneumonia were fever, cough, and myalgia or
fatigue with abnormal chest CT, and the less common symptoms
were sputum production, headache, hemoptysis, and diarrhea
4–6
.
This new infectious agent is more likely to affect older males to
cause severe respiratory diseases
7,8
. Some of the clinical
symptoms were different from the severe acute respiratory
syndrome (SARS) caused by SARS coronavirus (SARS-CoV) that
happened in 2002–2003, indicating that a new person-to-person
transmission infectious agent has caused this emergent viral
pneumonia outbreak
8,9
. Chinese researchers have quickly isolated
a new virus from the patient and sequenced its genome (29,903
nucleotides)
10
. The infectious agent of this viral pneumonia
happenening in Wuhan was finally identified as a novel
coronavirus (2019-nCOV), the seventh member of the family of
coronaviruses that infect humans
11
. On 11th February 2020, WHO
named the novel viral pneumonia as “Corona Virus Disease
(COVID19)”, while the international Committee on Taxonomy of
Viruses (ICTV) suggested this novel coronavirus name as “SARS-
CoV-2”due to the phylogenetic and taxonomic analysis of this
novel coronavirus
12
.
CHARACTERISTICS OF 2019 NOVEL CORONAVIRUS
Coronaviruses belong to the family of Coronaviridae, of the order
Nidovirales, comprising large, single, plus-stranded RNA as their
genome
13,14
. Currently, there are four genera of coronaviruses: α-
CoV, β-CoV, γ-CoV, and δ-CoV
15,16
. Most of the coronavirus can
cause the infectious diseases in human and vertebrates. The α-CoV
and β-CoV mainly infect the respiratory, gastrointestinal, and
central nervous system of humans and mammals, while γ-CoV and
δ-CoV mainly infect the birds
13,17–19
.
Usually, several members of the coronavirus cause mild
respiratory disease in humans; however, SARS-CoV and the Middle
East respiratory syndrome coronavirus (MERS-CoV) explored in
2002–2003 and in 2012, respectively, caused fatal severe
respiratory diseases
20–22
. The SARS-CoV and MERS-CoV belong to
the β-CoV
23,24
. 2019-nCoV explored in Wuhan also belongs to the
β-CoV according to the phylogenetic analysis based on the viral
genome
10,11
. Although the nucleotide sequence similarity is less
than 80% between 2019-nCoV and SARS-CoV (about 79%) or
MERS-CoV (about 50%), 2019-nCoV can also cause the fetal
infection and spread more faster than the two other corona-
viruses
7,9,11,25–27
. The genome nucleotide sequence identity
between a coronavirus (BatCoV RaTG13) detected in the bat
Rhinolophus affinis from Yunnan Province, China, and 2019-nCoV,
was 96.2%, indicating that the natural host of 2019-nCoV may also
be the Rhinolophus affinis bat
11
. However, the differences may also
suggest that there is an or more intermediate hosts between the
bat and human. A research team from the South China Agricultural
University has invested more than 1 000 metagenomic samples
Received: 15 February 2020 Revised: 18 February 2020 Accepted: 19 February 2020
1
State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases & Department of Cariology and Endodontics, West China Hospital of Stomatology,
Sichuan University, Chengdu, China
Correspondence: Xuedong Zhou (zhouxd@scu.edu.cn) or Biao Ren (renbiao@scu.edu.cn)
www.nature.com/ijos
International Journal of Oral Science
1234567890();,:
from pangolins, and found that 70% pangolins contained
β-CoV
28
. One of the coronaviruses they isolated from the
pangolins comprised a genome that was very similar with that
from 2019-nCoV, and the genome sequence similarity was 99%,
indicating that the pangolin may be the intermediate host of
2019-nCoV
29
.
2019-nCoV possessed the typical coronavirus structure with the
“spike protein”in the membrane envelope
30
, and also expressed
other polyproteins, nucleoproteins, and membrane proteins, such
as RNA polymerase, 3-chymotrypsin-like protease, papain-like
protease, helicase, glycoprotein, and accessory proteins
10,11,30
. The
S protein from coronavirus can bind to the receptors of the host to
facilitate viral entry into target cells
31,32
. Although there are four
amino acid variations of S protein between 2019-nCoV and SARS-
CoV, 2019-nCoV can also bind to the human angiotensin-
converting enzyme 2 (ACE2), the same host receptor for SARS-
CoV, as 2019-nCoV can bind to the ACE2 receptor from the cells
from human, bat, civet cat, and pig, but it cannot bind to the cells
without ACE2
11,33–35
. A recombinant ACE2-Ig antibody, a SARS-
CoV-specific human monoclonal antibody, and the serum from a
convalescent SARS-CoV-infected patient, which can neutralize
2019-nCoV, confirmed ACE2 as the host receptor for 2019-nCoV
36–39
.
The high affinity between ACE2 and 2019-nCoV S protein also
suggested that the population with higher expression of ACE2
might be more susceptible to 2019-nCoV
40,41
. The cellular serine
protease TMPRSS2 also contributed to the S-protein priming of
2019-nCoV, indicating that the TMPRSS2 inhibitor might constitute
a treatment option
36
.
THE POSSIBLE TRANSMISSION ROUTES OF 2019-NCOV
The common transmission routes of novel coronavirus include
direct transmission (cough, sneeze, and droplet inhalation
transmission) and contact transmission (contact with oral, nasal,
and eye mucous membranes)
42
. Although common clinical
manifestations of novel coronavirus infection do not include eye
symptoms, the analysis of conjunctival samples from confirmed
and suspected cases of 2019-nCoV suggests that the transmission
of 2019-nCoV is not limited to the respiratory tract
4
, and that eye
exposure may provide an effective way for the virus to enter the
body
43
.
In addition, studies have shown that respiratory viruses can be
transmitted from person to person through direct or indirect
contact, or through coarse or small droplets, and 2019-nCoV can
also be transmitted directly or indirectly through saliva
44
. Notably,
a report of one case of 2019-nCoV infection in Germany indicates
that transmission of the virus may also occur through contact with
asymptomatic patients
45
.
Studies have suggested that 2019-nCoV may be airborne
through aerosols formed during medical procedures
46
.Itis
notable that 2019-nCoV RNA could also be detected by rRT-PCR
testing in a stool specimen collected on day 7 of the patient’s
illness
47
. However, the aerosol transmission route and the
fecal–oral transmission route concerned by the public still need
to be further studied and confirmed.
POSSIBLE TRANSMISSION ROUTES OF 2019-NCOV IN DENTAL
CLINICS
Since 2019-nCoV can be passed directly from person to person by
respiratory droplets, emerging evidence suggested that it may
also be transmitted through contact and fomites
43,48
. In addition,
the asymptomatic incubation period for individuals infected with
2019-nCov has been reported to be ~1–14 days, and after 24 days
individuals were reported, and it was confirmed that those
without symptoms can spread the virus
4,5,49
. To et al. reported
that live viruses were present in the saliva of infected individuals
by viral culture method
43
. Furthermore, it has been confirmed that
2019-nCov enters the cell in the same path as SARS coronavirus,
that is, through the ACE2 cell receptor
25
. 2019-nCoV can
effectively use ACE2 as a receptor to invade cells, which may
promote human-to-human transmission
11
. ACE2
+
cells were
found to be abundantly present throughout the respiratory tract,
as well as the cells morphologically compatible with salivary gland
duct epithelium in human mouth. ACE2
+
epithelial cells of salivary
gland ducts were demonstrated to be a class early targets of SARS-
CoV infection
50
, and 2019-nCoV is likely to be the same situation,
although no research has been reported so far.
Dental patients and professionals can be exposed to pathogenic
microorganisms, including viruses and bacteria that infect the oral
cavity and respiratory tract. Dental care settings invariably carry
the risk of 2019-nCoV infection due to the specificity of its
procedures, which involves face-to-face communication with
patients, and frequent exposure to saliva, blood, and other body
fluids, and the handling of sharp instruments. The pathogenic
microorganisms can be transmitted in dental settings through
inhalation of airborne microorganisms that can remain suspended
in the air for long periods
51
, direct contact with blood, oral fluids,
or other patient materials
52
, contact of conjunctival, nasal, or oral
mucosa with droplets and aerosols containing microorganisms
generated from an infected individual and propelled a short
distance by coughing and talking without a mask
53,54
, and indirect
contact with contaminated instruments and/or environmental
surfaces
50
. Infections could be present through any of these
conditions involved in an infected individual in dental clinics and
hospitals, especially during the outbreak of 2019-nCoV (Fig. 1).
Airborne spread
The airborne spread of SARS-Cov (severe acute respiratory
syndrome coronavirus) is well-reported in many literatures. The
dental papers show that many dental procedures produce
aerosols and droplets that are contaminated with virus
55
. Thus,
droplet and aerosol transmission of 2019-nCoV are the most
important concerns in dental clinics and hospitals, because it is
hard to avoid the generation of large amounts of aerosol and
droplet mixed with patient’s saliva and even blood during dental
practice
53
. In addition to the infected patient’s cough and
breathing, dental devices such as high-speed dental handpiece
uses high-speed gas to drive the turbine to rotate at high speed
and work with running water. When dental devices work in the
patient’s oral cavity, a large amount of aerosol and droplets mixed
with the patient’s saliva or even blood will be generated. Particles
of droplets and aerosols are small enough to stay airborne for an
extended period before they settle on environmental surfaces or
enter the respiratory tract. Thus, the 2019-nCoV has the potential
to spread through droplets and aerosols from infected individuals
in dental clinics and hospitals.
Contact spread
A dental professional’s frequent direct or indirect contact with
human fluids, patient materials, and contaminated dental instru-
ments or environmental surfaces makes a possible route to the
spread of viruses
53
. In addition, dental professionals and other
patients have likely contact of conjunctival, nasal, or oral mucosa
with droplets and aerosols containing microorganisms generated
from an infected individual and propelled a short distance by
coughing and talking without a mask. Effective infection control
strategies are needed to prevent the spread of 2019-nCoV
through these contact routines.
Contaminated surfaces spread
Human coronaviruses such as SARS-CoV, Middle East Respiratory
Syndrome coronavirus (MERS-CoV), or endemic human corona-
viruses (HCoV) can persist on surfaces like metal, glass, or plastic
for up to a couple of days
51,56
. Therefore, contaminated surfaces
that are frequently contacted in healthcare settings are a potential
Transmission routes of 2019-nCoV and controls in dental practice
Peng et al.
2
International Journal of Oral Science (2020) 12:9
source of coronavirus transmission. Dental practices derived
droplets and aerosols from infected patients, which likely
contaminate the whole surface in dental offices. In addition, it
was shown at room temperature that HCoV remains infectious
from 2 h up to 9 days, and persists better at 50% compared with
30% relative humidity. Thus, keeping a clean and dry environment
in the dental office would help decrease the persistence of 2019-
nCoV.
INFECTION CONTROLS FOR DENTAL PRACTICE
Dental professionals should be familiar with how 2019-nCoV is
spread, how to identify patients with 2019-nCoV infection, and what
extra-protective measures should be adopted during the practice, in
order to prevent the transmission of 2019-nCoV. Here we
recommend the infection control measures that should be followed
by dental professionals, particularly considering the fact that
aerosols and droplets were considered as the main spread routes
of 2019-nCoV. Our recommendations are based on the Guideline for
the Diagnosis and Treatment of Novel Coronavirus Pneumonia
(the 5th edition) (http://www.nhc.gov.cn/yzygj/s7653p/202002/
3b09b894ac9b4204a79db5b8912d4440.shtml), the Guideline for the
Prevention and Control of Novel Coronavirus Pneumonia in Medical
Institutes (the 1st edition) (http://www.nhc.gov.cn/yzygj/s7659/
202001/b91fdab7c304431eb082d67847d27e14.shtml), and the
Guideline for the Use of Medical Protective Equipment in the Prevention
and Control of Novel Coronavirus Pneumonia (http://www.nhc.gov.cn/
yzygj/s7659/202001/e71c5de925a64eafbe1ce790debab5c6.shtml)
released by the National Health Commission of the People’s
Republic of China, and the practice experience in West China
Hospital of Stomatology related to the outbreak of 2019-nCoV
transmission.
Patient evaluation
First of all, dental professionals should be able to identify a
suspected case of COVID-19. To date that this paper was drafted,
the National Health Commission of the People’s Republic of China
has released the 5th edition of the Guideline for the Diagnosis and
Treatment of Novel Coronavirus Pneumonia. In general, a patient
with COVID-19 who is in the acute febrile phase of the disease is
not recommended to visit the dental clinic. If this does occur, the
dental professional should be able to identify the patient with
suspected 2019-nCoV infection, and should not treat the patient in
the dental clinic, but immediately quarantine the patient and
report to the infection control department as soon as possible,
particularly in the epidemic period of 2019-nCoV.
The body temperature of the patient should be measured in the
first place. A contact-free forehead thermometer is strongly
recommended for the screening. A questionnaire should be used
to screen patients with potential infection of 2019-nCoV before
they could be led to the dental chair-side. These questions should
include the following: (1) Do you have fever or experience fever
within the past 14 days? (2) Have you experienced a recent onset
of respiratory problems, such as a cough or difficulty in breathing
within the past 14 days? (3) Have you, within the past 14 days,
traveled to Wuhan city and its surrounding areas, or visited the
neighborhood with documented 2019-nCoV transmission? (4)
Have you come into contact with a patient with confirmed 2019-
nCoV infection within the past 14 days? (5) Have you come into
contact with people who come from Wuhan city and its
surrounding areas, or people from the neighborhood with recent
documented fever or respiratory problems within the past
14 days? (6) Are there at least two people with documented
experience of fever or respiratory problems within the last 14 days
having close contact with you? (7) Have you recently participated
in any gathering, meetings, or had close contact with many
unacquainted people?
If a patient replies “yes”to any of the screening questions, and
his/her body temperature is below 37.3 °C, the dentist can defer
the treatment until 14 days after the exposure event. The patient
should be instructed to self-quarantine at home and report any
fever experience or flu-like syndrome to the local health
department. If a patient replies “yes”to any of the screening
questions, and his/her body temperature is no less than 37.3 °C,
the patient should be immediately quarantined, and the dental
professionals should report to the infection control department of
the hospital or the local health department. If a patient replies
“no”to all the screening questions, and his/her body temperature
is below 37.3 °C, the dentist can treat the patient with extra-
protection measures, and avoids spatter or aerosol-generating
procedures to the best. If a patient replies “no”to all the screening
questions, but his/her body temperature is no less than 37.3 °C,
Susceptible individuals
Droplets
Droplets and aerosols
Dental professionals
Infected patient
Airborne
Contaminated surfaces
Direct contact
Indirect contact
Dental practice
Fig. 1 Illustration of transmission routes of 2019-nCoV in dental clinics and hospitals
Transmission routes of 2019-nCoV and controls in dental practice
Peng et al.
3
International Journal of Oral Science (2020) 12:9
the patient should be instructed to the fever clinics or special
clinics for COVID-19 for further medical care.
Hand hygiene
Fecal–oral transmission has been reported for 2019-nCoV, which
underlines the importance of hand hygiene for dental practice.
Although appropriate hand hygiene is the routine prerequisite for
dental practice, hand-washing compliance is relatively low, which
imposes a great challenge to the infection control during the
epidemic period of 2019-nCoV transmission. Reinforcement for
good hand hygiene is of the utmost importance. A two-before-
and-three-after hand hygiene guideline is proposed by the
infection control department of the West China Hospital of
Stomatology, Sichuan University, to reinforce the compliance of
hand washing. Specifically, the oral professionals should wash
their hands before patient examination, before dental procedures,
after touching the patient, after touching the surroundings and
equipment without disinfection, and after touching the oral
mucosa, damaged skin or wound, blood, body fluid, secretion, and
excreta. More caution should be taken for the dental professionals
to avoid touching their own eyes, mouth, and nose.
Personal protective measures for the dental professionals
At present, there is no specific guideline for the protection of
dental professionals from 2019-nCoV infection in the dental clinics
and hospitals. Although no dental professional has been reported
to acquire 2019-nCoV infection to the date the paper was drafted,
the last experience with the SARS coronavirus has shown vast
numbers of acquired infection of medical professionals in hospital
settings
57
. Since airborne droplet transmission of infection is
considered as the main route of spread, particularly in dental
clinics and hospitals, barrier-protection equipment, including
protective eyewear, masks, gloves, caps, face shields, and
protective outwear, is strongly recommended for all healthcare
givers in the clinic/hospital settings during the epidemic period of
2019-nCoV.
Based on the possibility of the spread of 2019-nCoV infection,
three-level protective measures of the dental professionals are
recommended for specific situations. (1) Primary protection
(standard protection for staff in clinical settings). Wearing
disposable working cap, disposable surgical mask, and working
clothes (white coat), using protective goggles or face shield, and
disposable latex gloves or nitrile gloves if necessary. (2) Secondary
protection (advanced protection for dental professionals). Wearing
disposable doctor cap, disposable surgical mask, protective
goggles, face shield, and working clothes (white coat) with
disposable isolation clothing or surgical clothes outside, and
disposable latex gloves. (3) Tertiary protection (strengthened
protection when contact patient with suspected or confirmed
2019-nCoV infection). Although a patient with 2019-nCoV infec-
tion is not expected to be treated in the dental clinic, in the
unlikely event that this does occur, and the dental professional
cannot avoid close contact, special protective outwear is needed.
If protective outwear is not available, working clothes (white coat)
with extra disposable protective clothing outside should be worn.
In addition, disposable doctor cap, protective goggles, face shield,
disposable surgical mask, disposable latex gloves, and imperme-
able shoe cover should be worn.
Mouthrinse before dental procedures
A preoperational antimicrobial mouthrinse is generally believed to
reduce the number of oral microbes. However, as instructed by
the Guideline for the Diagnosis and Treatment of Novel Coronavirus
Pneumonia (the 5th edition) released by the National Health
Commission of the People’s Republic of China, chlorhexidine,
which is commonly used as mouthrinse in dental practice, may
not be effective to kill 2019-nCoV. Since 2019-nCoV is vulnerable
to oxidation, preprocedural mouthrinse containing oxidative
agents such as 1% hydrogen peroxide or 0.2% povidone is
recommended, for the purpose of reducing the salivary load of
oral microbes, including potential 2019-nCoV carriage. A pre-
procedural mouthrinse would be most useful in cases when
rubber dam cannot be used.
Rubber dam isolation
The use of rubber dams can significantly minimize the production
of saliva- and blood-contaminated aerosol or spatter, particularly
in cases when high-speed handpieces and dental ultrasonic
devices are used. It has been reported that the use of rubber dam
could significantly reduce airborne particles in ~3-foot diameter of
the operational field by 70%
58
. When rubber dam is applied, extra
high-volume suction for aerosol and spatter should be used
during the procedures along with regular suction
59
. In this case,
the implementation of a complete four-hand operation is also
necessary. If rubber dam isolation is not possible in some cases,
manual devices, such as Carisolv and hand scaler, are recom-
mended for caries removal and periodontal scaling, in order to
minimize the generation of aerosol as much as possible.
Anti-retraction handpiece
The high-speed dental handpiece without anti-retraction valves
may aspirate and expel the debris and fluids during the dental
procedures. More importantly, the microbes, including bacteria
and virus, may further contaminate the air and water tubes within
the dental unit, and thus can potentially cause cross-infection. Our
study has shown that the anti-retraction high-speed dental
handpiece can significantly reduce the backflow of oral bacteria
and HBV into the tubes of the handpiece and dental unit as
compared with the handpiece without anti-retraction function
60
.
Therefore, the use of dental handpieces without anti-retraction
function should be prohibited during the epidemic period of
COVID-19. Anti-retraction dental handpiece with specially
designed anti-retractive valves or other anti-reflux designs are
strongly recommended as an extra preventive measure for cross-
infection
59
. Therefore, the use of dental handpieces without anti-
retraction function should be prohibited during the epidemic
period of COVID-19. Anti-retraction dental handpiece with
specially designed anti-retractive valves or other anti-reflux
designs are strongly recommended as an extra preventive
measure for cross-infection.
Disinfection of the clinic settings
Medical institutions should take effective and strict disinfection
measures in both clinic settings and public area. The clinic settings
should be cleaned and disinfected in accordance with the Protocol
for the Management of Surface Cleaning and Disinfection of Medical
Environment (WS/T 512-2016) released by the National Health
Commission of the People’s Republic of China. Public areas and
appliances should also be frequently cleaned and disinfected,
including door handles, chairs, and desks. The elevator should be
disinfected regularly. People taking elevators should wear masks
correctly and avoid direct contact with buttons and other objects.
Management of medical waste
The medical waste (including disposable protective equipment
after use) should be transported to the temporary storage area of
the medical institute timely. The reusable instrument and items
should be pretreated, cleaned, sterilized, and properly stored in
accordance with the Protocol for the Disinfection and Sterilization of
Dental Instrument (WS 506-2016) released by the National Health
Commission of the People’s Republic of China. The medical and
domestic waste generated by the treatment of patients with
suspected or confirmed 2019-nCoV infection are regarded as
infectious medical waste. Double-layer yellow color medical waste
package bags and “gooseneck”ligation should be used. The
surface of the package bags should be marked and disposed
Transmission routes of 2019-nCoV and controls in dental practice
Peng et al.
4
International Journal of Oral Science (2020) 12:9
according to the requirement for the management of
medical waste.
SUMMARY
Since December 2019, the newly discovered coronavirus (2019-
nCov) has caused the outbreak of pneumonia in Wuhan and
throughout China. 2019-nCov enters host cells through human
cell receptor ACE2, the same with SARS-CoV, but with higher
binding affinity
61
. The rapidly increasing number of cases and
evidence of human-to-human transmission suggested that the
virus was more contagious than SARS-CoV and MERS-CoV
9,25,27,61
.
By mid-February 2020, a large number of infections of medical
staff have been reported
62
, and the specific reasons for the failure
of protection need to be further investigated. Although clinics
such as stomatology have been closed during the epidemic, a
large number of emergency patients still go to the dental clinics
and hospitals for treatment. We have summarized the possible
transmission routes of 2019-nCov in stomatology, such as the
airborne spread, contact spread, and contaminated surface
spread. We also reviewed several detailed practical strategies to
block virus transmission to provide a reference for preventing the
transmission of 2019-nCov during dental diagnosis and treatment,
including patient evaluation, hand hygiene, personal protective
measures for the dental professionals, mouthrinse before dental
procedures, rubber dam isolation, anti-retraction handpiece,
disinfection of the clinic settings, and management of
medical waste.
ACKNOWLEDGEMENTS
This study was supported by the Emergency Project of Sichuan University
(0082604151013, XZ).
AUTHOR CONTRIBUTIONS
X.Z. conceived and designed the structure of this review; X.Z., X.X., X.P., Y.L., and B.R.
wrote the paper; X.Z. revised the paper.
ADDITIONAL INFORMATION
Competing interests: The authors declare no competing interests.
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