SARS-CoV-2 contact tracing among disadvantaged populations during epidemic intervals should be a priority strategy: results from a pilot experiment in Barcelona

Abstract

Objectives The aim of this study was to trace contacts of COVID-19 hospitalised patients and determine the risk factors of infection in urban areas. Study design Longitudinal analysis of contacts identified from index cases. Methods A contact tracing study was carried out in the Northern Metropolitan area of Barcelona, Spain, during the inter-epidemic lapse of May to July 2020, a period of low SARS-CoV-2 incidence. Index cases were notified from the referral hospital. Contacts were traced and followed-up for 14 days. Reverse transcription polymerase chain reaction (RT-PCR) was performed at day 0 and day 14 for contacts. Results In total, 368 contacts were identified from 81 index cases (median of 7 contacts per index case), from which 308 were traced successfully. The median age of contacts was of 28 years old, 62% (223 of 368) were males and 28 were non-nationals (34.1%). During the follow-up period, 100 contacts tested positive for COVID-19 (32.5% [95% confidence interval {CI} = 27.3–38.0]), with a secondary infection rate of 48.3% (95% CI = 40.8–55.9) among housemates. Clusters of index and respective contacts tended to aggregate within disadvantaged neighbourhoods (p < 0.001), and non-national index cases resulted in higher secondary infection rates compared with nationals (51.0% [95% CI = 41.0–60.9] vs 22.3% [95% CI = 16.8–28.8]; p < 0.001). Conclusions Disadvantaged communities experience a disproportionate burden of COVID-19 and may act as infection reservoirs. Contact tracing with a cross-cutting approach among these communities is required, especially during inter-epidemic periods.

SARS-CoV-2 Secondary Attack Rates in Vaccinated and Unvaccinated Household Contacts during Replacement of Delta with Omicron Variant, Spain

“…Our results show a high SAR among household contacts for both the Delta-dominant (58.2%) and Omicron-dominant (80.9%) periods; we found a 2-to 6-fold higher risk of infection for household contacts of symptomatic index case-patients during the Omicron-dominant period. SARs in our study were higher than that observed in a previous study conducted in the same geographic area in 2020, which showed a secondary infection rate of 48.3% when the ancestral SARS-CoV-2 strain responsible for the first infection wave was predominant (9). This previous study (9) classified hospitalized persons as index case-patients, and the mapping of those index cases demonstrated clear clustering in geographic areas with lower socioeconomic status.…”

“…SARs in our study were higher than that observed in a previous study conducted in the same geographic area in 2020, which showed a secondary infection rate of 48.3% when the ancestral SARS-CoV-2 strain responsible for the first infection wave was predominant (9). This previous study (9) classified hospitalized persons as index case-patients, and the mapping of those index cases demonstrated clear clustering in geographic areas with lower socioeconomic status. In our study, we did not observe geographic aggregation of index case-patients and Vaccine evasion might be a contributor to the higher transmissibility of the Omicron variant in areas with high vaccine coverage (F.P.…”

Factors Associated With Household Transmission of SARS-CoV-2

“…This updated systematic review and meta-analysis found that, with the addition of 37 studies, 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 the estimated overall household SAR of SARS-CoV-2 was 18.9%, which is similar to the estimate in the previous review. 1 Nonetheless, when analyzing SAR by study period, we observed an increase in household transmission over time.…”

“…China or Singapore 22 12,14,17,27,46,47,49-56,59,60,62-64,67,75,84a 14.4 (11.8-17.4) Other 65 [4][5][6][7][8][9][10][11]13,15,16,[18][19][20][21][22][23][24][25][26][28][29][30][31][32][33][34][35][36][37][38][39][40]45,48,57,58,61,65,66,[68][69][70][71][72][73][74][76][77][78][79]…”

“…Characteristics of Studies Included in Analysis of Household Secondary Attack Rates for SARS-CoV-2 (continued) ,23,24,29,37,40,45,79,[88][89][90]92 21.0(13.8-30.6) No 75[4][5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21][22][25][26][27][28][30][31][32][33][34][35][36][37][38][39][74][75][76][77][78][80][81][82][83][84]…”