90,000 children and adults in Spain, including 2,460 from the Balearic Islands, are being invited to take part in a new study to determine the prevalence of coronavirus infection, by determining antibodies against the virus by autonomous community, province, age and sex.
The seroprevalence study has been prepared by the Ministry of Health, the Carlos III Health Institute, the National Statistics Institute and the Autonomous Communities and has been approved by the ISCIII Ethics Committee.
Changes in prevalence will be used to monitor the evolution of the epidemic, particularly new infections derived from community transmission.
Of the 90,000 participants, 45,000 will be analysed in the 52 provinces.
15,000 will be analysed in the 17 autonomous communities.
The remaining 30,000 people will be distributed proportionally according to the population of each province, as follows.
1,200 in Álava, 1,260 in Albacete, 2,400 in Alicante, 1,380 in Almería, 2,400 in Asturias, 1,020 in Ávila.
1,860 in Badajoz, 5,160 in Barcelona, 1,200 in Burgos.
1,440 in Cáceres, 1,800 in Cádiz, 2,100 in Cantabria, 1,320 in Castellón, 900 in Ceuta, 1,380 in Ciudad Real, 1,440 in Córdoba, 1,980 in A Coruña, 1,080 in Cuenca.
1,440 in Girona, 1,560 in Granada, 1,140 in Guadalajara, 1,620 in Guipúzcoa.
1,260 in Huelva, 1,140 in Huesca.
1,320 in Jaén.
1,320 in León, 1,200 in Lleida and 1,980 in La Rioja, 1,200 in Lugo.
6,000 in Madrid, 2,100 in Malaga, 900 in Melilla, 2,700 in Murcia.
2,160 in Navarra.
1,140 in Ourense.
1,020 in Palencia, 2,040 in Las Palmas, 1,800 in Pontevedra.
1,200 in Salamanca, 1,020 Segovia, 2,340 in Seville, 960 in Soria.
1,500 in Tarragona, 1,980 in Tenerife, 1,020 in Teruel, 1,620 in Toledo.
2,940 in Valencia, 1,380 in Valladolid, 2,040 in Vizcaya, 1,020 in Zamora and 2,160 in Zaragoza.
In order to optimise fieldwork and avoid excessive sample dispersion, the sub-sample corresponding to each stratum of municipal size is selected in two successive stages.
First, census tracts (first-stage sampling units) are randomly selected with probability proportional to their size, and 24 households (second-stage units) are subsequently sampled within each selected census tract using simple random sampling.
Finally, all people residing in the home will be invited to participate in the study.
Members of selected households will be contacted by 'phone to inform them about the objectives of the study, request their consent and arrange a home visit. To assess potential selection bias, socio-demographic information will also be collected from people who decline to participate in the study.
All of the children and adults who participate will undergo a rapid immuno-chromatography test to determine whether they have antibodies in their blood.
The test being used is the 'Orient Gene Covis 19 IgM/IgG', from Zhejiang Orient Gene Biotech, with CE marking which uses colloidal gold immuno-chromatography in point-of-care format, in blood, serum/plasma samples, detects both IgM and IgG, and the results will be known within 10 minutes.
The working document states that there are two reliability studies with this test that show sensitivity figures greater than 80% and specificity close to 99% in serum and blood whether obtained by venipuncture or digital puncture.
A serum antibody measurement test will also be carried out by Healthcare Personnel on participants who agree to give a blood sample. Quantification of serum IgG antibodies will be carried out by means of an enzyme immuno-adsorption assay, (the selection and removal of specific antibodies and immune complexes.)
Epidemiological Survey
Each selected home and each participant will be asked to complete an epidemiological questionnaire in order to document any previous diagnosis of Covid-19, or the presence or history of any symptoms.
In this way, the participants will be classed as negative, asymptomatic or possible past or present Covid-19.
Each participant will be asked for permission to access their medical history, so that in the second phase the data of those selected in the sample can be incorporated into the study.
The epidemiological questionnaire will be completed online to make the process faster and easier and the information will be collected on a central database along with the data from the rapid tests to allow instantaneous monitoring of all information.
The National Epidemiology Centre will carry out the analysis with the support of the INE, to help field teams monitor control measures in homes.
It’s estimated that in the first round of fieldwork it will take 2 weeks to collect all the information from 36,000 households in 1,500 census sections.
To guarantee that the census sections are equally represented in both weeks, 12 households from each section will be randomly selected to be analysed during the first week, which will constitute Cohort A (18,000 households), and the remaining 12 households from each section will be analysed in the second week, constituting Cohort B (18,000 households).
It is estimated that at least three rounds of follow-up, separated by one week, will be necessary to solve possible logistical problems and process all of the information.
Cohort A will always be visited in the first week of each round and Cohort B in the second week.
How You Are Invited To Participate
Participants will be contacted by ‘phone. If a home has more than one phone and the call is not answered, the following number and successive numbers will be used to maximise the possibility of contact. If no response is obtained to any of the numbers, the operation will be repeated a minimum of 5 times at different times of the day and if none of them are successful, the address will be classified as unreachable.
In the following waves of the study, the attempt to locate these addresses that continue to be part of the sample universe of the study will be repeated and included in the corresponding wave as long as they agree to participate.
Once telephone contact has been established, the participants will be advised of the objective and characteristics of the study and asked if they're willing to participate. Once the information and characteristics about everyone living at the address has been obtained an interview appointment will be set up.
Information will also be collected about household members who need a certificate to justify absence from work to take part in the study.
The results of the seroprevalence study will be known at the end of next week.