Figure 1. As time goes by, severity declines. Time (days after
first case) correlates negatively with the duration of symptoms (in
days) for patients younger than 60 years (circles) and older than 59
years (triangles) during the first COVID-19 outbreak in an isolated
population.
Case fatality and thus possibly also disease severity of COVID-19
patients may be linked with length of follow up period (Rossi et al.,
2020). However, in our small study population follow up is essentially
continuous. Possible explanations for the observed decline in disease
severity are improved anti-inflammatory treatments towards the end of
the outbreak, changes in population susceptibility or pathogen
virulence, less severe cases showing up later in time, or an effect of
lockdown on viral burden or infective doses with subsequent effects of
disease severity.
The COVID-19 pandemic presents numerous challenges to epidemiologists
and health authorities. The ongoing de-escalation process in Spain will
provide information on the most likely mechanisms explaining our
observation. If the decline in severity is due to the lockdown, case
severity and duration are expected to grow during de-escalation. In this
case, only effective contact tracing followed by testing and case
isolation should serve to control further outbreaks. However, if host-
or pathogen-related factors are involved, this would represent good news
since it might facilitate softer disease control interventions.
Nevertheless, these observations will contribute to combating the
current coronavirus pandemic, its aftermath and potential future
clustered outbreaks or comparable healthcare emergencies.
Contributors
FR and CG planned the study. Data were collected by FR and CG. Data
analysis was led by LD and JdF. All authors interpreted the study
findings, contributed to the manuscript, and approved the final version
for publication.
Declaration of interests
We declare no competing interests.
Acknowledgments
This study had no specific funding. We would like to thank the local
veterinarian Javier Camarena and the municipality of Horcajo de los
Montes for information provided. We acknowledge UCLM support to Grupo
SaBio.
Ethical statement
The authors confirm that the ethical policies of the journal, as noted
on the journal’s author guidelines page, have been adhered to. No
ethical approval was required as this study was based on official
records and anonymized. FR had full access to all the data in the study
and all authors had final responsibility for the decision to submit for
publication.
Data availability
The data that support the findings of this study are available from the
corresponding author upon reasonable request.