Estimating the cumulative incidence of SARS-CoV-2 infection in Costa Rica: modelling seroprevalence data in a population-based cohort

Background

The true incidence of SARS-CoV-2 infection in Costa Rica was likely much higher than officially reported, because infection is often associated with mild symptoms and testing was limited by official guidelines and socio-economic factors.

Methods

Using serology to define natural infection, we developed a statistical model to estimate the true cumulative incidence of SARS-CoV-2 in Costa Rica early in the pandemic. We estimated seroprevalence from 2223 blood samples collected from November 2020 to October 2021 from 1976 population-based controls from the RESPIRA study. Samples were tested for antibodies against SARS-CoV-2 nucleocapsid and the receptor-binding-domain of the spike proteins. Using a generalized linear model, we estimated the ratio of true infections to officially reported cases. Applying these ratios to officially reported totals by age, sex, and geographic area, we estimated the true number of infections in the study area, where 70% of Costa Ricans reside. We adjusted the seroprevalence estimates for antibody decay over time, estimated from 1562 blood samples from 996 PCR-confirmed COVID-19 cases.

Findings

The estimated total proportion infected (ETPI) was 4.0 times higher than the officially reported total proportion infected (OTPI). By December 16th, 2021, the ETPI was 47% [42-52] while the OTPI was 12%. In children and adolescents, the ETPI was 11.0 times higher than the OTPI.

Interpretation

Our findings suggest that nearly half the population had been infected by the end of 2021. By the end of 2022, it is likely that a large majority of the population had been infected.

Funding

This work was sponsored and funded by the National Institute of Allergy and Infectious Diseases through the National Cancer Institute, the Science, Innovation, Technology and Telecommunications Ministry of Costa Rica, and Costa Rican Biomedical Research Agency-Fundacion INCIENSA (grant N/A).

[Sero-epidemiological survey on hepatitis B virus in Yunnan province, between 2006 and 2014]

Objective: Through two nationwide sero-epidemiological survey programs on hepatitis B virus (HBV), hepatitis B markers in Yunnan province were compared between the findings in 2014 and in 2006. Results were used to understand the HBV epidemic status in Yunnan province and to estimate the efficiency of measures on prevention and control of the disease. Methods: People at the age of 1-29 years were sampled from 6 counties of the National Disease Surveillance sites in Yunnan province, by multi-stage random sampling method. Demographic information was collected by questionnaire, and 2-4 ml serum sample was taken to detect HBsAg, anti-HBs, anti-HBc, HBeAg and anti-HBe, by ELISA method. Results: were logged-in the database and analyzed by SPSS 17.0. Results Between the two studies, no statistically significant differences were observed on the overall HBV infection rates and the positive rates of HBsAg, HBeAg, anti-HBe, anti-HBc. Positive rate of anti-HBs in 2014 was significantly higher than that in 2006. The main two combination profiles of hepatitis B markers were through the fifth model which was positive only for anti-HBs and the sixth model which was negative for all markers in 2006, and the same in 2014. Detection rate through the fifth profile in 2014 was significantly higher than the rate in 2006, while the detection rate of the sixth profile in 2014 was significantly lower than the one in 2006. When analyzing the differences in the same age group, between the two surveys, results showed that the positive rate of anti-HBs in 2014 was significantly higher than that in 2006, in both the10-14 and the 15-19 years-old groups. Positive rate of anti-HBc in the 20-29 year-olds in 2014 was significantly lower than the one of 2006. The positive rates of HBsAg in the age groups of 1-4, 5-14 and 15-29 were 1.12%,1.61% and 1.25% respectively, in 2014. Conclusion: Prevention and control measures on HBV seemed in great progres. However, more effective prevention and control measures should be taken continually among people under the age of 15, in Yunnan province.