Serological surveillance reveals a high exposure to SARS-CoV-2 and altered immune response among COVID-19 unvaccinated Cameroonian individuals

Abstract

Surveillance of COVID-19/SARS-CoV-2 dynamics is crucial to understanding natural history and providing insights into the population's exposure risk and specific susceptibilities. This study investigated the seroprevalence of SARS-CoV-2 antibodies, its predictors, and immunological status among unvaccinated patients in Cameroon. A multicentre cross-sectional study was conducted between January and September 2022 in the town of Douala. Patients were consecutively recruited, and data of interest were collected using a questionnaire. Blood samples were collected to determine Immunoglobin titres (IgM and IgG), interferon gamma (IFN- γ) and interleukin-6 (IL-6) by ELISA, and CD4+ cells by flow cytometry. A total of 342 patients aged 41.5 ± 13.9 years were included. Most participants (75.8%) were asymptomatic. The overall crude prevalence of IgM and IgG was 49.1% and 88.9%, respectively. After adjustment, the seroprevalence values were 51% for IgM and 93% for IgM. Ageusia and anosmia have displayed the highest positive predictive values (90.9% and 82.4%) and specificity (98.9% and 98.3%). The predictors of IgM seropositivity were being diabetic (aOR = 0.23, p = 0.01), frequently seeking healthcare (aOR = 1.97, p = 0.03), and diagnosed with ageusia (aOR = 20.63, p = 0.005), whereas those of IgG seropositivity included health facility (aOR = 0.15, p = 0.01), age of 40-50 years (aOR = 8.78, p = 0.01), married (aOR = 0.21, p = 0.02), fever (aOR = 0.08, p = 0.01), and ageusia (aOR = 0.08, p = 0.01). CD4+, IFN-γ, and IL-6 were impaired in seropositive individuals, with a confounding role of socio-demographic factors or comorbidities. Although the WHO declared the end of COVID-19 as a public health emergency, the findings of this study indicate the need for continuous surveillance to adequately control the disease in Cameroon.

Fig 1. Flow diagram of the study.

COVID-19: Coronavirus disease 2019, Ig: Immunoglobulin, CD: Cluster of differentiation, IFN-γ: Interferon gamma, IL-6: Interleukin 6.

Fig 2

Proportion of unvaccinated patients (A), and serum levels of IgM (B) and IgG (C) by COVID-19 vaccination status. The one-way analysis of variance (ANOVA) and Duncan’s post-hoc tests were used to make pairwise comparisons between groups. In Fig 2B and 2C, only statistically significant comparisons were showed on the graphs. *Statistically significant at p-value < 0.05.

Fig 3. Crude prevalence of SARS–CoV–2 antibodies by study sites.

The map was generated using AcgGIS v8.1 software (Esri, Redlands, CA, USA) and GraphPad version 5.03 for Windows (GraphPad PRISM, San Diego, Inc., California, USA). The pie charts depict the prevalence of patients positive for IgM (black section), IgG (pink section) and IgG + IgM (purple section). *For Deido district hospital, the sample collection site was located in Bonamoussadi neighbourhood. ** For Bangue district hospital, the sample collection site was located in Akwa neighbourhood.

Fig 4. Crude prevalence of SARS–CoV–2 antibodies by main clinical symptoms.

Ig: Immunoglobulin, n.s: Not significant, SARS–CoV–2: Severe acute respiratory syndrome coronavirus 2. Each bar represents the proportion of patients seropositive with respect to clinical symptoms. Only symptoms with occurrence > 15 were included in the analysis. Pearson’s independence chi-square and Fisher’s exact tests were used to compare percentages. *Statistically significant at *p-value < 0.05, **p-value < 0.01, and *** p-value < 0.0001.

Fig 5. Overall variation of CD4+ (A, D), IFN-γ (B, E) and IL-6 (C, F) with respect to presence of anti-SARS-CoV-2 IgM and IgG antibodies.

Ig: Immunoglobulin, IL-6: Interleukin 6, IFN-γ: Interferon gamma, CD: Cluster of differentiation. The parametric unpaired sample Student’s t-test, and non-parametric Mann-Whitney test ere used to compare the groups. *Statistically significant at p-value < 0.05.

Fig 6. Variation of CD4+, INF-γ and IL-6 by seropositivity status, demographic, clinical, and comorbidity information.

Ig: Immunoglobulin, SARS–CoV–2: Severe acute respiratory syndrome coronavirus 2, IL-6: Interleukin 6, IFN-γ: Interferon gamma, CD: Cluster of differentiation. The number of participants in each group are presented in round brackets. The non-parametric unpaired sample Student’s t-test was used to compare the groups. *Statistically significant at p-value < 0.05.