tetano
Editor, Senior Moderator
Front Public Health
. 2024 Sep 10:12:1429021.
doi: 10.3389/fpubh.2024.1429021. eCollection 2024. Personal characteristics and transmission dynamics associated with SARS-CoV-2 semi-quantitative PCR test results: an observational study from Belgium, 2021-2022
Toon Braeye[SUP] 1 2 [/SUP], Kristiaan Proesmans[SUP] 3 [/SUP], Dieter Van Cauteren[SUP] 1 [/SUP], Ruben Brondeel[SUP] 1 [/SUP], Niel Hens[SUP] 2 4 [/SUP], Elias Vermeiren[SUP] 1 [/SUP], Naïma Hammami[SUP] 5 [/SUP], Angel Rosas[SUP] 6 [/SUP], Adrae Taame[SUP] 7 [/SUP], Emmanuel André[SUP] 8 9 [/SUP], Lize Cuypers[SUP] 8 9 [/SUP]
Affiliations
Introduction: Following harmonization efforts by the Belgian National Reference Center for SARS-CoV-2, semi-quantitative PCR test (SQ-PCR) results, used as a proxy for viral load, were routinely collected after performing RT-qPCR tests.
Methods: We investigated both the personal characteristics associated with SQ-PCR results and the transmission dynamics involving these results. We used person-level laboratory test data and contact tracing data collected in Belgium from March 2021 to February 2022. Personal characteristics (age, sex, vaccination, and laboratory-confirmed prior infection) and disease stage by date of symptom onset were analyzed in relation to SQ-PCR results using logistic regression. Vaccine effectiveness (VE) against a high viral load (≥10[SUP]7[/SUP] copies/mL) was estimated from the adjusted probabilities. Contact tracing involves the mandatory testing of high-risk exposure contacts (HREC) after contact with an index case. Odds ratios for test positivity and high viral load in HREC were calculated based on the SQ-PCR result of the index case using logistic regression models adjusted for age, sex, immunity status (vaccination, laboratory-confirmed prior infection), variant (Alpha, Delta, Omicron), calendar time, and contact tracing covariates.
Results: We included 909,157 SQ-PCR results of COVID-19 cases, 379,640 PCR results from index cases, and 72,052 SQ-PCR results of HREC. High viral load was observed more frequently among recent cases, symptomatic cases, cases over 25 years of age, and those not recently vaccinated (>90 days). The vaccine effectiveness (VE) of the primary schedule in the first 30 days after vaccination was estimated at 47.3% (95%CI 40.8-53.2) during the Delta variant period. A high viral load in index cases was associated with an increased test positivity in HREC (OR 2.7, 95%CI 2.62-2.79) and, among those testing positive, an increased likelihood of a high viral load (OR 2.84, 95%CI 2.53-3.19).
Keywords: SARS-CoV-2; contact tracing; epidemiology; transmission; vaccine effectiveness; viral load.
. 2024 Sep 10:12:1429021.
doi: 10.3389/fpubh.2024.1429021. eCollection 2024. Personal characteristics and transmission dynamics associated with SARS-CoV-2 semi-quantitative PCR test results: an observational study from Belgium, 2021-2022
Toon Braeye[SUP] 1 2 [/SUP], Kristiaan Proesmans[SUP] 3 [/SUP], Dieter Van Cauteren[SUP] 1 [/SUP], Ruben Brondeel[SUP] 1 [/SUP], Niel Hens[SUP] 2 4 [/SUP], Elias Vermeiren[SUP] 1 [/SUP], Naïma Hammami[SUP] 5 [/SUP], Angel Rosas[SUP] 6 [/SUP], Adrae Taame[SUP] 7 [/SUP], Emmanuel André[SUP] 8 9 [/SUP], Lize Cuypers[SUP] 8 9 [/SUP]
Affiliations
- PMID: 39319296
- PMCID: PMC11420023
- DOI: 10.3389/fpubh.2024.1429021
Introduction: Following harmonization efforts by the Belgian National Reference Center for SARS-CoV-2, semi-quantitative PCR test (SQ-PCR) results, used as a proxy for viral load, were routinely collected after performing RT-qPCR tests.
Methods: We investigated both the personal characteristics associated with SQ-PCR results and the transmission dynamics involving these results. We used person-level laboratory test data and contact tracing data collected in Belgium from March 2021 to February 2022. Personal characteristics (age, sex, vaccination, and laboratory-confirmed prior infection) and disease stage by date of symptom onset were analyzed in relation to SQ-PCR results using logistic regression. Vaccine effectiveness (VE) against a high viral load (≥10[SUP]7[/SUP] copies/mL) was estimated from the adjusted probabilities. Contact tracing involves the mandatory testing of high-risk exposure contacts (HREC) after contact with an index case. Odds ratios for test positivity and high viral load in HREC were calculated based on the SQ-PCR result of the index case using logistic regression models adjusted for age, sex, immunity status (vaccination, laboratory-confirmed prior infection), variant (Alpha, Delta, Omicron), calendar time, and contact tracing covariates.
Results: We included 909,157 SQ-PCR results of COVID-19 cases, 379,640 PCR results from index cases, and 72,052 SQ-PCR results of HREC. High viral load was observed more frequently among recent cases, symptomatic cases, cases over 25 years of age, and those not recently vaccinated (>90 days). The vaccine effectiveness (VE) of the primary schedule in the first 30 days after vaccination was estimated at 47.3% (95%CI 40.8-53.2) during the Delta variant period. A high viral load in index cases was associated with an increased test positivity in HREC (OR 2.7, 95%CI 2.62-2.79) and, among those testing positive, an increased likelihood of a high viral load (OR 2.84, 95%CI 2.53-3.19).
Keywords: SARS-CoV-2; contact tracing; epidemiology; transmission; vaccine effectiveness; viral load.