Serial population-based serosurveys for COVID-19 in two neighbourhoods of Karachi, Pakistan

Muhammad Imran Nisar, Nadia Ansari, Farah Khalid, Mashal Amin, Hamna Shahbaz, Aneeta Hotwani, Najeeb Rehman, Sierra Pugh, Usma Mehmood, Arjumand Rizvi, Arslan Memon, Zahoor Ahmed, Ashfaque Ahmed, Junaid Iqbal, Ali Faisal Saleem, Uzma Bashir Aamir, Daniel B. Larremore, Bailey Fosdick, Fyezah Jehan

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24 Citations (Scopus)


Objective: To determine population-based estimates of coronavirus disease 2019 (COVID-19) in a densely populated urban community of Karachi, Pakistan. Methods: Three cross-sectional surveys were conducted in April, June and August 2020 in low- and high-transmission neighbourhoods. Participants were selected at random to provide blood for Elecsys immunoassay for detection of anti-severe acute respiratory syndrome coronavirus-2 antibodies. A Bayesian regression model was used to estimate seroprevalence after adjusting for the demographic characteristics of each district. Results: In total, 3005 participants from 623 households were enrolled in this study. In Phase 2, adjusted seroprevalence was estimated as 8.7% [95% confidence interval (CI) 5.1–13.1] and 15.1% (95% CI 9.4–21.7) in low- and high-transmission areas, respectively, compared with 0.2% (95% CI 0–0.7) and 0.4% (95% CI 0–1.3) in Phase 1. In Phase 3, it was 12.8% (95% CI 8.3–17.7) and 21.5% (95% CI 15.6–28) in low- and high-transmission areas, respectively. The conditional risk of infection was 0.31 (95% CI 0.16–0.47) and 0.41 (95% CI 0.28–0.52) in low- and high-transmission neighbourhoods, respectively, in Phase 2. Similar trends were observed in Phase 3. Only 5.4% of participants who tested positive for COVID-19 were symptomatic. The infection fatality rate was 1.66%, 0.37% and 0.26% in Phases 1, 2 and 3, respectively. Conclusion: Continuing rounds of seroprevalence studies will help to improve understanding of secular trends and the extent of infection during the course of the pandemic.

Original languageEnglish
Pages (from-to)176-182
Number of pages7
JournalInternational Journal of Infectious Diseases
Publication statusPublished - May 2021


  • Antibody
  • COVID-19
  • Pakistan
  • Seroepidemiology
  • Seroprevalence
  • Surveillance


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