COVID-19 and lombardy: TESTing the impact of the first wave of the pandemic

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Abstract

BACKGROUND: Italy was the first western country to experience a large Coronavirus Disease 2019 (COVID-19) outbreak and the province of Bergamo experienced one of the deadliest COVID-19 outbreaks in the world. Following the peak of the epidemic in mid-March, the curve has slowly fallen thanks to the strict lockdown imposed by the Italian government on 9th March 2020.

METHODS: We performed a cross-sectional study to assess the prevalence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection in 423 workers in Bergamo province who returned to the workplace after the end of the Italian lockdown on 5th May 2020. To this end, we performed an enzyme-linked immunosorbent assay (ELISA) to detect the humoral response against SARS-CoV-2 and a nasopharyngeal swab to assess the presence of SARS-CoV-2 RNA by real-time reverse transcription polymerase chain reaction (rRT-PCR). As a secondary aim of the study, we validated a lateral flow immunochromatography assay (LFIA) for the detection of anti-SARS-CoV-2 antibodies.

FINDINGS: ELISA identified 38.5% positive subjects, of whom 51.5% were positive for both IgG and IgM, 47.3% were positive only for IgG, but only 1.2% were positive for IgM alone. Only 23 (5.4%) participants tested positive for SARS-CoV-2 by rRT-PCR, although with high cycle thresholds (between 34 and 39), indicating a very low residual viral load that was not able to infect cultured cells. All these rRT-PCR positive subjects had already experienced seroconversion. When the ELISA was used as the comparator, the estimated specificity and sensitivity of the rapid LFIA for IgG were 98% and 92%, respectively.

INTERPRETATION: the prevalence of SARS-CoV-2 infection in the province of Bergamo reached 38.5%, significantly higher than has been reported for most other regions worldwide. Few nasopharyngeal swabs tested positive in fully recovered subjects, though with a very low SARS-CoV-2 viral load, with implications for infectivity and discharge policies for positive individuals in the post-pandemic period. The rapid LFIA used in this study is a valuable tool for rapid serologic surveillance of COVID-19 for population studies.

FUNDING: The study was supported by Regione Lombardia, Milano Serravalle - Milano Tangenziali S.p.A., Brembo S.p.A, and by MEI System.

Original languageEnglish
Pages (from-to)103069
JournalEBioMedicine
Volume61
DOIs
Publication statusPublished - Nov 2020

Keywords

  • Adult
  • Antibodies, Viral/blood
  • Betacoronavirus/genetics
  • COVID-19
  • Coronavirus Infections/diagnosis
  • Cross-Sectional Studies
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Humans
  • Immunoglobulin G/blood
  • Immunoglobulin M/blood
  • Italy/epidemiology
  • Male
  • Middle Aged
  • Nasopharynx/virology
  • Pandemics
  • Pneumonia, Viral/diagnosis
  • RNA, Viral/genetics
  • Real-Time Polymerase Chain Reaction
  • SARS-CoV-2
  • Viral Load

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