For coronavirus disease 2019 (COVID-19), frequently reported symptoms in nonseverely
sick patients include fever, fatigue, and dry cough.
1
However, infected patients may not exhibit symptoms. Some patients may be presymptomatic
and develop symptoms later in the disease course whereas others remain asymptomatic,
but either group can be infectious.
2,3
Hence, asymptomatic carriers and presymptomatic individuals may be potential sources
of nosocomial transmission. As such, consideration can be given to testing asymptomatic
patients upon admission to the hospital. The Infectious Diseases Society of America
(IDSA) guidelines on the diagnosis of COVID-19 recommend against testing of asymptomatic
hospitalized patients in low-prevalence (<2%) settings.
4
This recommendation is based on expert opinion and lacks supporting evidence.
The city of Hamilton, Ontario, Canada, has a population of 580,000 and qualified as
a low-prevalence area at the time of this study. The average number of daily new cases
identified was 1.9 per 100,000 population.
5
For hospital admission, the testing strategy was (and continues to be) based on symptoms
or exposures.
6
Within this low-prevalence setting, we conducted a multicenter point-prevalence study
to evaluate the utility of severe acute respiratory coronavirus virus 2 (SARS-CoV-2)
testing of asymptomatic patients in terms of capturing positive cases that would be
missed by symptom-based testing on admission.
Methods
We conducted a point-prevalence study across 4 tertiary acute-care hospitals in Hamilton
from April 15 to April 21, 2020. The Hamilton Integrated Research Ethics Board approved
this study (no. 10894).
COVID-19 testing on admission
According to provincial guidelines, testing was based on the following symptoms: fever,
new or worsening acute respiratory illness symptom (ie, cough, dyspnea, sore throat,
runny nose or sneezing, nasal congestion, hoarse voice, difficulty swallowing, new
olfactory or taste disorder(s), nausea or vomiting, diarrhea, abdominal pain), or
clinical or radiological evidence of pneumonia.
6
Atypical presentations included unexplained fatigue or malaise, delirium, falls, acute
functional decline, exacerbation of chronic conditions, chills, headache, croup, tachycardia,
decrease in blood pressure, hypoxia, and lethargy.
6
At the time of this study, a patient with any of the above symptoms or exposure underwent
nasopharyngeal swab testing for SARS-CoV-2 upon admission to the hospital.
6
Patient inclusion
On the point-prevalence testing date, all adult inpatients were tested once if they
were admitted for 7–14 days, regardless of symptoms or prior negative SARS-CoV-2 test
result. Patients with a known positive SARS-CoV-2 test were excluded.
Testing on days 7–14 was based on the estimated median incubation period of 4 days
(interquartile range, 2–7 days).
7
Testing after the median incubation period would have captured most COVID-19 cases,
even if the exposure occurred as late as the day of admission.
Testing procedure
The nasopharyngeal swabs were collected, and a polymerase-chain reaction assay for
the SARS-CoV-2 envelope and 5’-untranslated region genes was performed at the local
virology laboratory in the hospital. This assay was validated against the provincial
standard testing.
Data collection
Data were extracted from the patient electronic chart system, which included demographics,
admitting diagnosis, hospital location, admitting service, reason for admission, Charlson
comorbidity index,
8
prior SARS-CoV-2 test result, chest imaging, and other microbiology test results.
On the day of testing, patients were assessed for symptoms, as listed above.
6
Results
Across the 4 hospitals, 125 inpatients were tested for SARS-CoV-2 (Table 1). Also,
5 patients (4.0%) had fever and 3 patients (2.4%) had respiratory symptoms at the
time of their test.
Table 1.
Patient Characteristics
Characteristic
Patients Tested(N = 125),No. (%)
a
Demographics
Age, median y (IQR)
77.0 (65.0–84.0)
Male
58 (46.4)
Location prior to admission
Community
94 (75.2)
Hospital
16 (12.8)
Retirement home
11 (8.8)
Long term care home
4 (3.2)
Hospitals
b
A
52 (41.6)
B
30 (24.0)
C
29 (23.2)
D
14 (11.2)
Location within hospital
Ward
95 (76.0)
ICU
8 (6.4)
Rehabilitation, palliative, or chronic care
22 (17.6)
Admitting service
Medicine
49 (39.2)
Surgery
30 (24.0)
Hematology oncology, medical oncology
16 (12.8)
ICU
8 (6.4)
Obstetrics
1 (0.8)
Other
21 (16.8)
Most common reason for admission
Hip fracture
11 (8.8)
Solid tumor–related complication
11 (8.8)
Stroke
7 (5.6)
Weakness or fall
7 (5.6)
Delirium or confusion
7 (5.6)
Charlson comorbidity index
0
18 (14.4)
1
15 (12.0)
2
28 (22.4)
3
18 (14.4)
≥4
46 (36.8)
Immunosuppressed
c
21 (16.8)
Symptoms at testing
Fever
5 (4.0)
Respiratory symptoms
3 (2.4)
Clinical or radiographic features of pneumonia
14 (11.2)
Atypical symptoms
10 (8.0%)
Chest imaging
Chest X-ray
92 (73.6)
CT chest image
26 (20.8)
Last chest imaging findings
Consolidation
34 (27.2)
Intralobular lines
1 (0.8)
Organizing pneumonia
0 (0)
Days from admission to testing, median (IQR)
11.0 (9.0–13.0)
SARS-CoV-2 test result
Negative
124 (99.2)
Positive
1 (0.8)
Prior SARS-CoV-2 testing done and negative
85 (68.0)
Days from prior SARS-CoV-2 test to current test
10.0 (8.0–12.0)
Testing for other respiratory viruses
d
Negative
86 (68.8)
Positive
0 (0)
Not done
39 (31.2)
Note. IQR, interquartile range; ICU, intensive care unit; CT, computed tomography.
a
Units unless otherwise specified.
b
The hospital sites include a 607-bed hospital that is the regional cardiac surgery
and neurosurgery center; a 228-bed hospital that is the regional center for cancer
care and bone marrow transplant; a 250-bed hospital that specializes in chronic care
and rehabilitation; and a 426-bed hospital that specializes in dialysis and renal
transplant.
c
Immunosuppression includes any of the following: chemotherapy, steroid therapy, neutropenia
with absolute neutrophil count <0.5, active hematological malignancy, HIV, primary
immunodeficiency, or solid organ or hematopoietic stem cell transplant requiring immunosuppressive
therapy.
d
Other respiratory viruses include influenza A and B, respiratory syncytial virus (RSV),
human metapneumovirus, parainfluenza virus types 1 and 3, adenovirus, rhinovirus,
and enterovirus.
Only 1 patient (0.8%) was positive for SARS-CoV-2. This patient presented to hospital
C reporting 2 weeks of fever and cough. A chest x-ray showed an ill-defined opacity
in the left lower lobe. The patient was initially isolated for acute respiratory illness.
Isolation was discontinued on admission day 2 after the SARS-CoV-2 test came back
negative, and the patient was treated for a presumptive bacterial pneumonia. The following
day, the patient was transferred to hospital D. The positive point-prevalence test
occurred on admission day 13 at hospital D. At the time of testing, the patient had
no new symptoms and the patient’s respiratory status continued to improve.
Discussion
In this point-prevalence study, 125 inpatients were tested, and only 1 patient (0.8%)
was positive for SARS-CoV-2. This positive case was symptomatic, and the patient had
had a prior SARS-CoV-2 test that was likely a false negative. He was initially isolated
for acute respiratory illness on presentation to the hospital. For COVID-19, infectiousness
has been estimated to decline quickly within 7 days,
9
so the patient was likely no longer infectious at the time of the second test. Therefore,
asymptomatic testing did not add any useful information or change infection control
practices compared to symptom-based screening.
To our knowledge, this is the first study to evaluate the benefit of asymptomatic
testing for hospitalized patients in a low-prevalence setting. In a New York hospital,
universal testing of women admitted for delivery showed 13.5% asymptomatic positive
SARS-CoV-2 results.
10
In contrast, our study found no asymptomatic positive cases. This finding is likely
due to differences in local prevalence.
The strengths of our study include the systematic approach to testing. Also, the inclusion
of 4 hospitals makes the results more generalizable. Our study has 2 limitations.
First, repeated point-prevalence testing would have yielded more precise results,
but this method would not have been feasible given the capacity of our virology laboratory.
Second, nasopharyngeal swabbing may produce false-negative results, given its estimated
sensitivity between 75% and 95%.
4
Although imperfect, nasopharyngeal swabbing is practical and is currently the recommended
test for asymptomatic patients.
4
In conclusion, our study suggests the minimal utility of asymptomatic testing in hospitalized
patients compared to symptom screening and targeted testing in low-prevalence settings,
which supports the current IDSA guidelines.
4