Household Transmission of SARS-CoV-2: A Prospective Longitudinal Study Showing Higher Viral Load and Increased Transmissibility of the Alpha Variant Compared to Previous Strains

We studied the secondary attack rate (SAR), risk factors, and precautionary practices of household transmission in a prospective, longitudinal study. We further compared transmission between the Alpha (B.1.1.7) variant and non-Variant of Concern (non-VOC) viruses. From May 2020 throughout April 2021, we recruited 70 confirmed COVID-19 cases with 146 household contacts. Participants donated biological samples eight times over 6 weeks and answered questionnaires. SARS-CoV-2 infection was detected by real-time RT-PCR. Whole genome sequencing and droplet digital PCR were used to establish virus variant and viral load. SARS-CoV-2 transmission occurred in 60% of the households, and the overall SAR for household contacts was 50%. The SAR was significantly higher for the Alpha variant (78%) compared with non-VOC viruses (43%) and was associated with a higher viral load. SAR was higher in household contacts aged ≥40 years (69%) than in younger contacts (40–47%), and for contacts of primary cases with loss of taste/smell. Children had lower viral loads and were more often asymptomatic than adults. Sleeping separately from the primary case reduced the risk of transmission. In conclusion, we found substantial household transmission, particularly for the Alpha variant. Precautionary practices seem to reduce SAR, but preventing household transmission may become difficult with more contagious variants, depending on vaccine use and effectiveness.

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Household transmission of SARS-CoV-2 in Norway; a prospective, longitudinal study showing increased transmissibility of the Alpha variant (B.1.1.7) compared with other variants

10.1101/2021.08.15.21261478 ◽

2021 ◽

Author(s):

Cathinka Halle Julin ◽

Anna Hayman Robertson ◽

Olav Hungnes ◽

Gro Tunheim ◽

Terese Bekkevold ◽

...

Keyword(s):

Risk Factors ◽

Longitudinal Study ◽

Close Contact ◽

Questionnaire Data ◽

Primary Case ◽

Prospective Longitudinal Study ◽

Household Contacts ◽

Household Transmission ◽

Alpha Variant ◽

Prospective Longitudinal

ABSTRACT Background We studied the secondary attack rate (SAR), risk factors, and precautionary practices of household transmission in a prospective longitudinal study. Moreover, we compared household transmission between the Alpha (B.1.1.7) variant and non-variants of concern (non-VOCs). Methods We recruited households of confirmed COVID-19 cases from May 2020 to May 2021. Households received 8 home visits over 6 weeks. Biological samples and questionnaire data were collected. Results We recruited 70 confirmed COVID-19 cases and 146 household contacts. Transmission occurred in 60% of the households; the overall SAR for household contacts was 49.6%. The SAR was significantly higher for the Alpha variant (77.8%) compared with non-VOC variants (42.5%) and was associated with a higher viral load. SAR was higher in household contacts aged ≥40 years (64%) than in younger contacts (40-47%), and for contacts of cases with loss of taste/smell. Close contact prior to confirmation of infection tended to give a higher SAR. A significantly lower SAR was found for sleeping separately from the primary case after confirmation of infection. Conclusion We found substantial household transmission, particularly for the Alpha variant. Precautionary practices seem to reduce SAR; however, prevention of transmission within households may become difficult with more transmissible variants.

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A prospective longitudinal study of tuberculosis among household contacts of smear-positive tuberculosis cases in Lima, Peru

BMC Infectious Diseases ◽

10.1186/s12879-016-1616-x ◽

2016 ◽

Vol 16 (1) ◽

Cited By ~ 7

Author(s):

Larissa Otero ◽

Lena Shah ◽

Kristien Verdonck ◽

Tullia Battaglioli ◽

Timothy Brewer ◽

...

Keyword(s):

Longitudinal Study ◽

Prospective Longitudinal Study ◽

Household Contacts ◽

Prospective Longitudinal

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Correlation of Viral Load and CD8 T-Lymphocytes with Development of Neurological Manifestations in Vertically HIV-1-Infected Infants. A Prospective Longitudinal Study

Neuropediatrics ◽

10.1055/s-2007-973490 ◽

1999 ◽

Vol 30 (04) ◽

pp. 197-204 ◽

Cited By ~ 16

Author(s):

D. Gurbindo ◽

S. Resino ◽

S. Sánchez-Ramón ◽

J. León ◽

M. Muñoz-Fernández

Keyword(s):

Viral Load ◽

Longitudinal Study ◽

T Lymphocytes ◽

Neurological Manifestations ◽

Prospective Longitudinal Study ◽

Cd8 T Lymphocytes ◽

Prospective Longitudinal ◽

Hiv 1

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Clinical and microbiological assessments of COVID-19 in healthcare workers: a prospective longitudinal study

10.1101/2020.11.04.20225862 ◽

2020 ◽

Author(s):

Antonin Bal ◽

Karen Brengel-Pesce ◽

Alexandre Gaymard ◽

Grégory Quéromès ◽

Nicolas Guibert ◽

...

Keyword(s):

Viral Load ◽

Longitudinal Study ◽

Symptom Onset ◽

Healthcare Workers ◽

Respiratory Pathogen ◽

Respiratory Pathogens ◽

Prospective Longitudinal Study ◽

Viral Shedding ◽

Viral Culture ◽

Prospective Longitudinal

BackgroundA comprehensive assessment of COVID-19 in healthcare workers (HCWs) including the investigation of viral shedding duration is critical.MethodsA longitudinal study including 319 HCWs was conducted. After SARS-CoV-2 screening with RT-PCR assay, other respiratory pathogens were tested with a multiplex molecular panel. For SARS-CoV-2 positive HCWs, the normalized viral load was determined weekly; viral culture and virus neutralization assays were also performed. For 190 HCWs tested negative, SARS-CoV-2 serological testing was performed one month after the inclusion.FindingsOf the 319 HCWs included, 67 (21.0%) were tested positive for SARS-CoV-2; two of them developed severe COVID-19. The proportion of smell and taste dysfunction was significantly higher in SARS-CoV-2 positive HCWs than in negative ones (38.8% vs 9.5% and 37.3% vs 10.7%, respectively, p<0.001). Of the 67 positive patients, 9.1% were tested positive for at least another respiratory pathogen (vs 19.5%, p=0.07). The proportion of HCWs with a viral load > 5.0 log10 cp/ml (Ct value <25) was less than 15% at 8 days after symptom onset; 12% of them were still positive after 40 days (Ct >37). More than 90% of culturable virus had a viral load > 4.5 log10 cp/ml (Ct < 26) and were collected within 10 days after symptom onset. From HCWs tested negative, 6/190 (3.2%) exhibited seroconversion for IgG antibodies.InterpretationOur data suggest that the determination of normalized viral load (or its estimation through Ct values) can be useful for discontinuing isolation of HCWs and facilitating their safe return to work. HCWs presenting mild COVID-19 are unlikely infectious 10 days after symptom onset.FundingFondation des Hospices Civils de Lyon. bioMérieux provided diagnostic kits.

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