Lecciones aprendidas de la investigación de un agrupamiento de la COVID-19
en Creil. Francia: efectividad de seleccionar casos sintomáticos y realizar un
rastreo de contactos a su alrededor.
Coronel Med. De Frank Laval. Francia
Lessons learned from the investigation of a COVID-19 cluster in Creil,
France: effectiveness of targeting symptomatic cases and conducting contact
Sanid. mil. 2022 79 (Extraordinario) 41
tracing around them
de Franck Laval1
BACKGROUND
This study presents the methods and results of the investigation
into a SARS-CoV-2 outbreak in a professional community. Due to
the limited testing capacity available in France at the time, we elab-orated
a testing strategy according to pre-test probability.
Methods
The investigation design combined active case finding and con-tact
tracing around each confirmed case, with testing of at-risk con-tact
persons who had any evocative symptoms (n = 88). One month
later, we performed serology testing to test and screen symptomatic
and asymptomatic cases again (n = 79).
RESULTS
Twenty-four patients were confirmed (14 with RT-PCR and 10
with serology). The attack rate was 29 % (24/83). Median age was
40 (24 to 59), and the sex ratio was 15/12. Only three cases were
asymptomatic (= no symptoms at all, 13 %, 95 % CI, 3-32). Nine-
1
teen symptomatic cases (79 %, 95 % CI, 63-95) presented a respira-tory
infection, two of which were severe. All the RT-PCR confirmed
cases acquired protective antibodies.
The median incubation was 3 days (from 1 to 11 days), and
the median generation interval was 3 days (0 to 12). We identified
pre-symptomatic transmission in 40 % of this cluster, but no trans-mission
from asymptomatic to symptomatic cases.
CONCLUSION
We report the effective use of targeted testing according to
pre-test probability, specifically prioritizing symptomatic COVID-
19 diagnosis and contact tracing. The asymptomatic rate raises
questions about the real role of asymptomatic infected people in
transmission. Conversely, pre-symptomatic contamination occurred
frequently in this cluster, highlighting the need to identify, test, and
quarantine asymptomatic at-risk contact persons (= contact trac-ing).
The local lockdown imposed helped reduce transmission dur-ing
the investigation period.
1 SSA (French Military Health Service), CESPA (French Armed Forces
Center for Epidemiology and Public Health), Marseille, France - franck.
de-laval@intradef.gouv.fr