Materials and methods
Cohort
Between 19th and 27th April 2020,
1170 military conscripts, 798 men (68. 2 %) and 372 women (31. 8 %)
were enrolled. Median age was 20 years (range 18 – 25). As conscripts
are called for military service regardless of residential area, our
cohort included men and women from all over Norway.
Extended systematic infection control
measures
The infection control measures performed by the Norwegian Armed Forces
Joint Medical Services are visualized in Figure 1.
Pre-enrollment measures
Two weeks prior to enrollment, the conscripts were interviewed by
telephone to motivate for military service and ensure compliance with
infection control measures related to COVID-19. All conscripts were
encouraged to conduct a self-imposed quarantine until enrollment.
Enrollment day questionnaires and
examinations
Initially on the enrollment day, each conscript was asked about current
respiratory symptoms, and body temperature was measured using an ear
thermometer. Individuals with symptoms and/or temperature ≥ 38, 0⁰ C
were further interviewed and clinically examined, and were then
quarantined pending the results of the PCR virus test (Figure 1).
All conscripts had to respond to an online questionnaire, focusing on
possible or confirmed COVID-19 over the past two weeks, compliance with
public infection control measures and possible close contact with
SARS-CoV-2 infected individuals.SARS-CoV-2 PCR specimen detection
At the enrollment day, nasopharyngeal swabs for
SARS-CoV-2 PCR specimen detection
were collected. PCR-tests were also performed after three and six weeks
of military training. The PCR tests were analyzed at the Department of
Microbiology at Oslo University Hospital using a Roche Cobas SARS-CoV-2
RNA test on the Cobas 6800 platform (Roche Diagnostics).
SARS-CoV-2 serologic
analyses
Venous blood was sampled using VACUETTE® Blood Collection Tubes (Greiner
bio-one) for SARS-CoV-2 serologic testing. Serologic tests were analyzed
at the Department of Microbiology at Oslo University Hospital using
Elecsys® anti-SARS-CoV-2 IgM/IgG assay fully automated on the Cobas e801
analyzer (Roche Diagnostics). The assay measures the combined total of
IgM and IgG against the nucleocapsid (N) structural protein of
SARS-CoV-2 and provides results as a cutoff index (COI) calculated based
on signal sample / assay cutoff. A COI above 1, 2 was defined as a
positive result.
Figure 1
SARS-COV-2 antibody rapid-test
Capillary blood was sampled for the Acro 2019-nCoV IgG/IgM rapid
antibody test (Acro Biotech, Inc.) at the enrollment day only, and the
test was performed on site. This rapid-test is a lateral flow
chromatographic immunoassay for qualitative detection of IgG and IgM
antibodies to SARS-CoV2. Individuals with a positive rapid-test went
through a clinical interview and examination, and were quarantined,
pending the results of the PCR virus test (Figure 1).
Ethics
Data from the extended systematic infection control are administered by
the Norwegian Armed Forces Health Registry (NAFHR). The NAFHR is a
central health registry with data from Norwegian Armed Forces personnel,
including conscripts and civilian and military staff employed by the
Armed Forces. The regulations for the Norwegian Armed Forces Health
Registry authorizes the NAFHR to produce statistics and research in
anonymous form 6.
Results
Enrollment day questionnaires and
examinations
On the enrollment day, 17 (1. 4 %) of the 1170 conscripts reported
having mild respiratory symptoms, and in addition nine conscripts (0, 8
%) had body temperature ≥ 38, 0⁰ C). None of these 26 were SARS-CoV-2
PCR positive or SARS-CoV-2 serology positive.
In the web-based questionnaire, 18 conscripts (1. 5 %) reported mild
respiratory symptoms during the past 14 days prior to enrollment.
Reported symptoms included runny nose and sneezing (72 %), stuffy nose
(61 %), cough (55 %), sore throat (33 %), headaches (33 %),
shortness of breath (16 %), fever (13 %), reduced sense of taste or
smelling (11 %), sore muscles (11 %) and dizziness (6 %). None of
these 18 conscripts were SARS CoV-2 PCR positive, but one had positive
SARS CoV-2 serology at enrollment.
Nine conscripts (0. 8 %) answered “yes” to the question “do you
think you have had COVID-19”. Among these, four conscripts were
SARS-CoV-2 serology positive and one was PCR positive.
SARS-CoV-2 PCR specimen detection
Two of the 1170 conscripts had positive PCR tests at enrollment and one
conscript with initial negative tests, tested positive at week six
(Table 1). None of these reported any symptoms during the two weeks
prior to or at enrollment, nor during the service period. However, based
on the clinical interview, the two conscripts who tested positive at
enrollment reported illness with symptom onset four and seven weeks
prior to enrollment, respectively. The individual who tested positive in
week six had not been ill, nor had he had any symptoms before or during
the six-week observation period.
Table 1
Figure 2