Low SARS‐CoV‐2 seroprevalence in a cohort of Brazilian sickle cell disease patients: Possible effects of emphasis on social isolation for a population initially considered to be at very high risk

Abstract Despite being initially considered at higher risk for severe COVID‐19, sickle cell disease (SCD) patients have mostly presented clinical severity similar to the general population. As their vulnerability to become infected remains uncertain, we assessed the seroreactivity for SARS‐CoV‐2 to estimate the prevalence of infection and possible phenotypic and socioeconomic determinants for their contagion. Serologic evaluation was performed on 135 patients with an overall prevalence of 11%; positivity was associated with older age and use of public transportation. We speculate that social distancing instructions recommended by our clinic may have contributed to lower levels of infection, but potential protection factors need further investigation.


INTRODUCTION
The high spread rate of the new coronavirus (SARS-CoV-2) has imposed massive challenges to health systems, especially considering the high potential of aggravation and mortality in specific populations, such as in the elderly and bearers of comorbidities [1]. In this context, patients with sickle cell disease (SCD) were expected to be at high risk for severe COVID-19, considering the damage in target organs such as the lungs and kidneys [2], which are also targeted in SARS-CoV-2 pathophysiology [3]. assessing the impact of COVID-19 on SCD patients, but with contradictory results regarding morbidity and mortality [4,5]. In fact, it is interesting to highlight that the series of cases published so far show an unexpected trend to milder presentations in SCD, with high fullrecovery rates [6][7][8].
Nevertheless, it is not yet possible to establish whether this mild picture is the standard to be observed in geographic locations other than the developed countries, such as Latin America and Africa, where the socioeconomic conditions and the access to health services tend to be precarious and can have a major impact on both the exposure to COVID-19 and the treatment of the basal condition. In face of these challenges, our service established protocol changes to minimize patient contact with the nosocomial environment and to favor social distancing, while maintaining the best possible assistance regarding both chronic and emergency care.
Thus, this study aimed to analyze the trend of seroreactivity for SARS-CoV-2 in SCD patients in a Brazilian Center and its distribution over time (August 2020 to January 2021), as well as its correlations with clinical and sociodemographic variables and the degree of social isolation actually achieved by these individuals.

Study population, questionnaire, and blood sampling
The study was conducted at the Hematology and Transfusion Medicine Center of the University of Campinas, a public reference center for the care of SCD in southeastern Brazil. Patients with any genotypic presentation (HbSS, Sβ-thalassemia, or HbSC) and above 18 years of age were

Laboratory tests
Samples were screened by chemiluminescence (reactivity considered positive: IgG ≥1.4 and IgM ≥1.0), according to the manufacturer's instructions (Abbott Architect, Ireland). Reagent samples were tested for the presence of neutralizing antibodies and their titration, as previously described [9]. After 3 days of incubation of Vero cells with patient serum-virus mixture, cells were inspected and the highest serum dilution that protected cells from cytopathic effect was taken as the neutralization titer.

Statistical analysis
Data are reported by frequency measures, and correlations of variables with positivity in serological tests were assessed using Fisher's exact test or t-test for independent samples.
Regarding serological evaluation, 57 patients (42%) were tested more than once during this period: 46 with two tests, 11 with ≥3 tests.

Protocol adaptations for care of SCD patients during COVID-19 pandemic and their possible impact on susceptibility
Social isolation of patients with hemoglobinopathies was recommended by our clinic, in line with national and international guidelines, considering that these patients could potentially develop severe SARS-CoV-2 infection. All routine appointments were canceled, and patients were encouraged to contact the center by phone or email at any time in case of whichever doubts they might have. Prescriptions for hydroxyurea, which are withdrawn at the public system, had their renewal period extended from 3 to 6 months. In addition, the center adopted a COVID-19 suspicion protocol at the entrance, avoiding the access of any individual with the slightest suspicion of infection or who had been in contact with a person presenting symptoms; those who presented symptoms were referred to a specific COVID-19 unit at the university hospital.
Appointments were maintained when the issue could not be solved over the phone: 65% of them comprised symptoms that required personalized assessment or laboratory propedeutic, followed by the evaluation for symptoms of worsening anemia (17%) or re-evaluation after recent hospital discharge (18%). transfusions, but was discharged after 14 days. There were no deaths during the study period and the average length of hospital stay was 6.25 days.
In this study's cohort, there were no correlations between serological positivity and education, income, number of household contacts, and maintenance of work outside the home; however, test positivity was associated with older age (40.3 × 22.9, p < .001) and regular use of public transport (Fisher exact test, p = .02).

DISCUSSION
This report highlights the importance of new measures of distant medical assistance for SCD in the context of a pandemic, which depends on the commitment of the medical team and confidence of the patients in this team. Therefore, interesting approaches have emerged, such as less bureaucracy in the dispensation of hydroxyurea and the occupation of secondary hospital beds that were not referenced for COVID assistance, for more immediate and personalized care. All these measures, taken together, provided less exposure for patients and maximized their social isolation, certainly contributing to a lower vulnerability to SARS-CoV-2 infection than initially projected. Therefore, we must emphasize that the lower availability of population testing in our country no doubt leads to a lower acknowledgment of cases. However, despite this fact, we were able to demonstrate that some patients had COVID-19 in such a benign form that they did not seek medical atten-