The first case of Middle East respiratory syndrome coronavirus (MERS-CoV) in the Republic
of Korea was confirmed in May 2015 after a traveller returned from the Middle East.
(
1
) There were 186 cases,
including 38 deaths, within two months. (
1
) The potential of a single MERS-confirmed patient to
result in such a large MERS outbreak constitutes a serious global health concern.
(
2
)
During this MERS outbreak, massive public health containment measures were enacted
at
various levels; these included epidemiological investigations, isolation of suspected
and confirmed cases, contact tracing and home quarantine of contacts. Local public
health centre (LPHC) and emergency medical services (EMS) personnel responded to the
outbreak by conducting initial interviews with suspected cases, transporting patients
and specimens and managing contacts. Responders in contact with patients used different
levels of personal protective equipment (PPE). Full-protection PPE includes a gown,
N95
respirator, gloves and goggles. As the transmissibility of MERS is unclear, (
3
) it is possible that responders
were infected by being exposed to MERS patients.
We conducted a cross-sectional study in January 2016 to assess whether LPHC and EMS
workers were infected and to determine their degree of exposure. The participants
had
contact with MERS-confirmed patients or their specimens during the outbreak and
volunteered to participate in this study. The survey, which was a face-to-face
interview, examined subjects’ general characteristics, professional
responsibilities, contact history, symptoms after exposure and use of PPE.
Contact was defined as meeting at least one of the following four criteria: (
4
) being within 2m of a confirmed
patient, staying in the same space as a confirmed patient for over 5 minutes,
contact with a patient’s respiratory or digestive secretions and contact with
specimens from confirmed patients before the sample was packaged. Contact within the
same space was graded into four levels according to distance of contact and wearing
of
PPE. Without full PPE protection: Grade 1 was defined as contact within 2m, and Grade
2
was defined as contact at over 2m. With full PPE protection: Grade 3 was defined as
contact within 2m, and Grade 4 was defined as contact at over 2m.
Serum collected from all participants was screened for the presence of MERS-CoV IgG
using
enzyme-linked immunosorbent assays (ELISAs). One sample with borderline results and
five
samples with negative ELISA results were retested using indirect immunofluorescence
(IIFT) and plaque reduction neutralization (PRNT) tests for confirmation. The indirect
ELISA and MERS-CoV IIFT used commercial MERS-CoV IIFT slides (EUROIMMUN, Lübeck,
Germany) and followed the manufacturer’s protocol. Analysis was performed using a
DE/Axio Imager M1 immunofluorescence microscope (Zeiss, Jena, Germany). The PRNT was
performed as previously described. (
5
) The number of plaques per well were counted; reductions
in plaque counts of 50% (PRNT50) and 90% (PRNT90) were calculated using the
Spearman-Kärber formula. (
5
)
Thirty-four workers participated in the study (
Table 1
): 31 from 11 LPHCs and three from two EMS
units. Twenty (58.8%) responders were male; their mean age was 44 (34–56.7)
years. Twenty-five participants (73.5%) occupied health-related positions: 11 (32.4%)
general health-care staff, 6 (17.6%) nurses, 4 (11.8%) doctors, 3 (8.8%) paramedics
and
1 medical laboratory technologist (2.6%). Nine participants (26.5%) were
non-health-related workers: 5 (14.7%) technicians, 2 (5.9%) administrators, 1 (2.9%)
agricultural worker and 1 (2.9%) unknown.
Table 1
Exposure to MERS-confirmed patients
(n = 34)
Exposure
n
(%)
Grade of
contact
Grade 1
7
(20.6)
Grade 2
3
(8.8)
Grade 3
20
(58.8)
Grade 4
4
(11.8)
Longest period
of contact
< 30
minutes
13
(38.2)
30 minutes to
1 hour
10
(29.4)
1 to
2 hour(s)
6
(17.6)
2 to
5 hours
5
(14.7)
Activity
(n = 67)*
Patient
transport
24
(35.8)
Patient
counselling
10
(14.9)
Ambulance
disinfection
10
(14.9)
Specimen
transportation
8
(11.9)
Respiratory
specimen collection
7
(10.4)
Taking vital
signs
4
(6.0)
Discarding
exposed goods
3
(4.5)
Other
1
(1.5)
Symptoms
after contact
Yes
1
(2.9)
No
33
(97.1)
PPE
education
Received
29
(85.3)
Not
received
5
(14.7)
Training in
wearing PPE
Received
20
(58.8)
Not
received
13
(38.2)
Unknown
1
(2.9)
* The 34 study participants performed multiple activities.
PPE: personal protective equipment.
Based on the highest risk contact for each participant, seven (20.6%) of the responders
were classified as Grade 1; they were partially protected with at least gloves and
an
N95 respirator (
Table 1
).
They contacted asymptomatic or symptomatic patients, and symptomatic patients wore
surgical masks. After MERS-CoV had been confirmed in a patient, all staff were fully
protected when in contact with the patient. The closest contact occurred when touching
and holding patients during transport. One responder wearing full PPE had a mild fever
(37.5 °C) after contact with a symptomatic patient who was later confirmed as
infected. Since the response system had not expanded in the early days of the outbreak,
she was not tested but was isolated with self-monitoring.
Serum samples were obtained from all 34 participants at an average of 7.3 months
(range: 6.7–8.1 months) after exposure. On ELISA, there were 33 (97.1%)
negative results and one borderline result. The results of six samples, including
one
with borderline ELISA results, were negative in the IIFT and PRNT.
In our study, we could not find evidence of MERS infection in the public health providers
after direct contact with confirmed patients. This may be because there was a lower
risk
of transmission when participants were transporting or counselling patients outside
of
the hospital compared to providing medical assistance within the hospital. In other
MERS
outbreaks, secondary infections were related to health-care settings. (
1
,
6
) Although the exact route of infection transmission
is unknown, aerosolizing procedures in crowded rooms with inadequate infection
prevention and control measures were observed in health-care settings. (
7
) In the 2015 Republic of Korea
outbreak, some health-care workers without proper PPE were infected in tertiary
hospitals, thus emphasizing the optimal use of PPE to prevent MERS infection. (
8
) Moreover, since the participants
did not contact any spreaders except one participant who contacted a patient that
caused
two secondary infections, the risk of transmission from the contacted patients was
likely low.
This study had several limitations. First, the survey was conducted 7.3 months
after the MERS outbreak, making recall bias possible. Second, it is possible that
we
missed some mild or asymptomatic cases. Furthermore, because the serological tests
were
performed several months post-exposure, pre-existing MERS antibodies may have decreased
or disappeared in the interval, potentially leading to underestimation. While
asymptomatic MERS infection had been detected using RT–PCR testing at the time of
outbreak, (
9
) a Saudi Arabian
study showed the longevity of MERS-CoV antibodies in MERS patients varied in the
severity of illness. For example, antibodies in severely infected patients persisted
after 18 months, but milder and subclinical cases detected no antibodies even early
on
in the disease. (
10
) Third, the
number of participants was relatively small and may not be representative or
generalizable. Despite these limitations, this study suggests that the risk of MERS
transmission to public health professionals responding to MERS outside the hospital
setting (i.e. patients’ homes) was low, particularly for those who wore some
level of PPE such as masks and gloves. Further study is needed to prospectively survey
public health responders including symptomatic or asymptomatic cases to conduct genetic
test and serologic test during an outbreak.
In conclusion, the public health providers in our study did not have evidence of MERS
transmission after direct contact with confirmed patients when PPE was used
properly.
Ethics
Ethical approval for the study was obtained from the institutional review board
of Seoul National University Hospital in Seoul (IRB No.
C-1512–049–727).