Observational, descriptive, and cross-sectional study with an analytical approach.

The study population consisted of 4050 teachers from early childhood education, primary, secondary, and high school levels from public, subsidized private, and private educational institutions located in the city of Bilbao (Basque Country, Spain), across 87 schools. The participants and source of information were the teachers, as they are the individuals best acquainted with the dynamics and social situation of students both individually and collectively, as well as being the key observers of compliance with COVID-19 measures throughout the educational day.

The entire study population was accessed. The sample size was estimated with a 95% confidence level, a population of 4050 teachers, and a 5% margin of error. Based on this, it was estimated that 352 valid responses were necessary.

The inclusion criteria were: educational institutions providing early childhood education, primary, secondary, and high school education located in the city of Bilbao, whether public, private subsidized, or private.

Exclusion criteria included: nurseries, vocational training centers, universities, official language schools, Basque language teaching centers (euskaltegis), and academies, irrespective of ownership.

The instrument used for data collection was an online, self-administered survey designed specifically for this study. It was not validated, as no validated questionnaires were available in our region for this purpose. The ad hoc questionnaire collected information on compliance with COVID-19 measures.

The questionnaire was administered between November 5, 2021, and January 5, 2022. To select the sample, the questionnaire was sent via email to the management team of each educational institution, who were then responsible for forwarding the questionnaire link to the teaching staff for completion. Data related to secondary variables or axes of inequality were collected from the Basque Institute of Statistics (18).

Descriptive analysis was performed, with qualitative variables expressed as frequencies and percentages, and quantitative variables expressed as means and standard deviations if normally distributed, or as medians and interquartile ranges if non-normally distributed. Additionally, bivariate analysis was conducted between sociodemographic variables and both primary and secondary variables. The chi-square test (χ^²), Fisher's test, Student's t-test, or the Mann-Whitney U test were used. Data were analyzed using SPSS software, version 21.0. The statistical significance level was set at α or Type I error of 5% (p < 0.05).

The study adhered to the basic ethical principles for clinical research, in accordance with the good clinical practice standards outlined in the Declaration of Helsinki (Fortaleza 2013) and the Oviedo Convention (1997). The handling, communication, and transfer of data complied with the provisions of the General Data Protection Regulation (GDPR) EU 2016/679 of the European Parliament and the Council of the European Union, dated April 27, 2016, which came into effect on May 25, 2018, and its incorporation into Spanish law through Organic Law 3/2018, of December 5, on the protection of personal data and the guarantee of digital rights. No personal data that could identify participants was collected, ensuring the confidentiality of the participants at all times (19,20).

Each participating teacher in the study freely and voluntarily signed the informed consent form online, after being provided with the study information sheet in advance. The study was reviewed and received a favorable opinion from the Research Ethics Committee of the Integrated Health Organization (OSI) Bilbao-Basurto (code: 104.21 CEICHUB) and was authorized by the Nursing Directorate of OSI Bilbao-Basurto for its execution and development.

The city of Bilbao has a population of 340,455 inhabitants, of which 10.1% are immigrants. Of the total population, 15.7% are under the age of 20. The municipality has a total area of 4059 hectares and is divided into 8 districts and 40 neighborhoods. It has a population density of 8387.7 inhabitants/km^², with an unemployment rate of 13.7%. Table 1 describes the demographic characteristics of the city of Bilbao by district.

Table 1. Table 1. Sociodemographic Variables Description (Axes of Inequality) of the City of Bilbao (Spain) Source: Based on data from the Basque Institute of Statistics.

The districts with the highest population are those occupying the central areas of the city (Ibaiondo, Abando, Deusto, and Rekalde), while the districts with the lowest population are the more peripheral ones (Otxarkoaga-Txurdinaga and Basurto-Zorroza). Similarly, the districts with the highest density are Abando and Begoña, while the districts with the lowest density are Basurto-Zorroza, Ibaiondo, Otxarkoaga-Txurdinaga, and Rekalde. Data on family income show significant differences between districts: Abando has the highest income, and Rekalde and Otxarkoaga-Txurdinaga have the lowest. On the other hand, Ibaiondo is the district with the highest percentage of immigrants, the highest percentage of emergency social aid, and the highest number of family households (Table 1).

The response rate was 24.7% among the total number of teachers in Bilbao, yielding 997 valid responses. Of the 87 educational institutions that met the inclusion criteria, representation was obtained from 81 of them (93.1%), with 47 (58.0%) being public, 30 (37.0%) subsidized private, and 4 (4.9%) private. By district, the number of participating schools was as follows: Deusto, 9 (11.1%); Uribarri, 10 (12.4%); Otxarkoaga-Txurdinaga, 14 (17.3%); Begoña, 7 (8.6%); Ibaiondo, 12 (14.8%); Abando, 15 (18.5%); Rekalde, 10 (12.4%); and Basurto-Zorroza, 4 (4.9%).

Regarding the 997 teachers who participated, significant differences were found based on the type of school (p < 0.0001), with 476 (47.7%) belonging to public schools, 510 (51.2%) to subsidized private schools, and 11 (1.1%) to private schools. By district, the number of teachers was as follows: Deusto, 139 (13.9%); Uribarri, 112 (11.2%); Otxarkoaga-Txurdinaga, 127 (12.7%); Begoña, 111 (11.1%); Ibaiondo, 156 (15.6%); Abando, 205 (20.6%); Rekalde, 110 (11.0%); and Basurto-Zorroza, 37 (3.7%).

By educational level, 118 teachers (11.8%) were from early childhood education, 396 (39.7%) from primary education, 330 (33.1%) from secondary education, and 153 (15.3%) from high school. Statistically significant differences were also found between districts and educational levels (p < 0.0001).

In general, a high percentage of positive responses regarding the compliance with anti-COVID-19 measures was observed, and statistically significant differences were found according to the educational level (p < 0.0001). Primary and high school teachers reported a higher percentage of compliance by almost all or all students (87.9% and 86.3%, respectively). In contrast, the early childhood education stage showed the lowest compliance rate, with only 68.7%.

Additionally, differences were found based on the type of educational institution (p = 0.001): private schools reported the highest degree of compliance by all or almost all students (100%), followed by subsidized private schools (88.1%) and public schools (77.7%). Similarly, differences were found by district (p = 0.006): Basurto-Zorroza and Otxarkoaga-Txurdinaga reported the lowest compliance by all or almost all students (64.8% and 78%, respectively) (Table 2).

Table 2. Table 2. General Compliance with COVID-19 Prevention and Control Measures

La figura 1 muestra los resultados en cuanto al grado de cumplimiento de cada medida (mascarillas, higiene de manos, distancias y ventilación) en función de la etapa educativa, tipo de centro educativo y distrito.

Figure 1. Figure 1. Greater versus lesser compliance with different anti-COVID-19 measures according to educational level, type of educational institution, and district

Regarding the distance between students within the classroom, statistically significant differences were found by educational stage (p < 0.0001). In this regard, 83.1% of early childhood education classrooms reported that the distance between students was less than 0.5 meters, while in primary education, secondary education, and high school, the most frequent response was a distance between 0.5 and 1 meter, with 45.5%, 49.7%, and 41.8%, respectively. Similarly, there were differences between student distances in the classroom and the type of educational institution (p < 0.0001). Public schools reported a higher rate of responses indicating distances between students of 0.5 and 1 meter (42.6%), followed by subsidized private schools (41.8%), while private schools reported distances between 1.5 and 2 meters as the most frequent between their students (45.5%). Finally, differences were found between the distance between students in the classroom and districts (p = 0.002), with the Otxarkoaga-Txurdinaga district having the highest proportion of students maintaining the recommended distance of at least 1.5 meters (Table 5).

Natural ventilation was present across all educational levels, regardless of the type of educational institution, with no significant differences found (p = 0.792 and p = 0.198, respectively). In line with this, there were also no statistically significant differences between natural ventilation and district (p = 0.254) (Table 5).

Artificial ventilation was absent across all educational levels, although differences were found based on the type of educational institution (p < 0.0001). It was more frequently present in private schools (45.5%), followed by subsidized private schools (9.8%) and public schools (1.3%). Additionally, differences were found for the presence of artificial ventilation by district (p < 0.0001), with Otxarkoaga-Txurdinaga (14.2%) having the highest presence and Basurto-Zorroza (0.0%) the lowest (Table 5). However, when analyzing the district of Otxarkoaga-Txurdinaga by its two neighborhoods, the presence of artificial ventilation was concentrated in Txurdinaga (100%) but absent in Otxarkoaga (0.0%).

Table 5. Table 5. Compliance with COVID-19 Prevention and Control Measures: Distances and Ventilation (n = 997)