Covert cases of Severe Acute Respiratory Syndrome Coronavirus 2: An obscure but present danger in regions endemic for Dengue and Chikungunya viruses

Abstract

Background: The impact of SARS-CoV-2 in regions endemic for both Dengue and Chikungunya is still not fully understood. Considering that symptoms/clinical features displayed during Dengue, Chikungunya and SARS-CoV-2 acute infections are similar, undiagnosed cases of SARS-CoV-2 in co-endemic areas may be more prevalent than expected. This study was conducted to assess the prevalence of covert cases of SARS-CoV-2 among samples from patients with clinical symptoms compatible with either Dengue or Chikungunya viral infection in the state of Espírito Santo, Brazil.

Methods: Presence of immunoglobulin G (IgG) antibody specific to SARS-CoV-2 nucleoprotein was detected using a chemiluminescent microparticle immunoassay in samples from 7,370 patients, without previous history of COVID-19 diagnosis, suspected of having either Dengue (n = 1,700) or Chikungunya (n = 7,349) from December 1st, 2019 to June 30th, 2020.

Findings: Covert cases of SARS-CoV-2 were detected in 210 (2.85%) out of the 7,370 serum samples tested. The earliest undiagnosed missed case of COVID-19 dated back to a sample collected on December 18, 2019, also positive for Dengue Virus. Cross-reactivity with either Dengue virus or other common coronaviruses were not observed.

Interpretation: Our findings demonstrate that concomitant Dengue or Chikungunya outbreaks may difficult the diagnosis of SARS-CoV-2 infections. To our knowledge, this is the first study to demonstrate, with a robust sample size (n = 7,370) and using highly specific and sensitive chemiluminescent microparticle immunoassay method, that covert SARS-CoV-2 infections are more frequent than previously expected in Dengue and Chikungunya hyperendemic regions. Moreover, our results suggest that SAR-CoV-2 cases were occurring prior to February, 2020, and that these undiagnosed missed cases may have contributed to the fast expansion of SARS-CoV-2 outbreak in Brazil. Data presented here demonstrate that in arboviral endemic regions, SARS-CoV-2 infection must be always considered, regardless of the existence of a previous positive diagnosis for Dengue or Chikungunya.

Fig 1. Characteristics of the Dengue, Chikungunya and SARS-CoV-2 outbreaks in the state of Espírito Santo from October 2019 to June 2020.

A) Number of Dengue, Chikungunya and SARS-CoV-2 positive cases in Espírito Santo over time; B) Positivity rate of Dengue, Chikungunya and SARS-CoV-2 cases over time.

Fig 2

A-C) Assessment of gender influence on immunoreactivity levels in Chikungunya, Dengue, and SARS-CoV-2 patients. A) Chikungunya patients; B) Dengue patients; and C) SARS-CoV-2 patients. Categorical variables were compared using Fisher’s exact test and continuous variables with the Mann-Whitney U test; *p<0.05; **p<0.01. 2D) Evolution of SARS-CoV-2 positivity rate from December 2019 to June 2020; 2E and F) Assessment of SARS-CoV-2 IgG immunoreactivity index (S/CO) categorized by: E) days post-symptoms onset, and F) grouped by age.

Fig 3

Correlation between SARS-CoV-2 IgG immunoreactivity index (S/CO), and both: A) age distribution (years). The black dotted line represents the cutoff point for the CMIA (S/CO = 1.4). B) time between symptoms onset and sample collection. No significant differences were observed. Rho (ᴩ) = 0.019 (Fig 3A) and 0.1111 (Fig 3B).

Fig 4

Assessment of pre-pandemic Dengue positive samples (PPS): A) Pre-pandemic samples (n = 84 samples) were tested using Abbott’s Architect SARS-CoV-2 IgG CMIA, 42 samples were from the acute phase and another 42 paired samples from the convalescent phase. The red dotted line represents the cutoff point for the CMIA (S/CO = 1.4); B) SARS-CoV-2 IgG immunoreactivity index (S/CO) displayed by acute samples and convalescent samples from Dengue positive patients. No significant differences were observed.

Fig 5. Distribution of the 210 positive cases of SARS-CoV-2 in the state of Espírito Santo.

The red and black location markers represent the date of sample collection. The municipalities in dark blue represent the localities with cases of Chikungunya only, and municipalities in light blue where both Chikungunya and Dengue.

Fig 6

A) Frequency of positive SARS-CoV-2 cases over time (December, 2019 to June, 2020). SARS-CoV-2 cases were grouped in SARS-CoV-2-only (red bars), co-infected with Chikungunya (blue bars) or co-infected with Dengue virus (green bars). B) SARS-CoV-2 IgG immunoreactivity index (S/CO) was compared between groups SARS-CoV-2-only (red dots), and co-infected with Chikungunya (blue dots) or Dengue (green dots). No significant differences were observed.

Fig 7. IgM immunoreactivity index in the presence or absence of SARS-CoV-2 IgG antibodies.

A) Chikungunya positive cases. B) Dengue positive cases. Continuous variables were compared with the Mann-Whitney U test; ***p<0.0001.