Results
We registered one-hundred and five school absences during the study, 43
in the first study period (spring 2022), and 62 in the last one (autumn
2022) (Supplementary Figure 1 ). Among these, we could obtain
data related to the diagnosis in 98 (93%) cases, the rest of them were
lost during the follow-up of the absence. Seventy-one absences were
respiratory-related and 27 were due to other causes, mainly with
gastrointestinal symptoms (66.7%). Among the absences due to RTI, the
most were upper RTI (56/71, 78.9%), and only six (8.5%) were confirmed
infections, 2 caused by influenza virus and 4 due to SARS-CoV-2
infection. These results represent a RTI incidence of 15.9 and 33.1
cases per 100 population in the first and second study period,
respectively. The maximum weekly RTI incidence was of 10.2 cases per 100
population in December 12-18, 2022.
The clinical, epidemiological and environmental characteristics of study
sample are summarized in table 1 , categorized by type of
absence (respiratory versus non-respiratory). We found a statistically
significant association with absences due to RTI when someone else at
home had respiratory symptoms (OR=9.12, CI 95%=2.54-33.39). We found a
positive association between higher median levels of CO2at class and respiratory-related absences (OR=1.2, CI 95%=0.98-1.46).
Moreover, there were more respiratory absences in autumn (OR=2.4, CI
95%=0.97-5.94). However, these last two associations did not reach
statistical significance at a level of 0.05; although their p-values
were lower than 0.1.
No other epidemiological risk factors were associated with RTI
incidence, such as household floor level, number of people living at
home, living with smokers, having any comorbidity or being vaccinated
against COVID-19.
Finally, in Figure 1 , we present the symptomatology of absences
belonging to each of the two latent classes. We can see that in the
first cluster, the most frequent symptoms were cough, nasal congestion
and fever, whereas in the second one, fever, gastrointestinal symptoms,
and fatigue predominated.