Factors Associated with HIV Coinfection among 440 Patients with Neurosyphilis: A Single-Center Retrospective Study from 2020 to 2025

Abstract Background Neurosyphilis patients with human immunodeficiency virus (HIV) coinfection present diagnostic and management challenges, yet features distinguishing HIV-coinfected from non-coinfected neurosyphilis patients remain incompletely characterized. We aimed to identify clinical and laboratory factors independently associated with HIV coinfection in this population. Methods This single-center retrospective study included 440 patients diagnosed with neurosyphilis between 2020 and 2025. Of these, 243 had neurosyphilis without HIV infection and 197 had HIV coinfection. We compared demographic characteristics, serum and cerebrospinal fluid (CSF) toluidine red unheated serum test (TRUST) results, CSF white blood cell counts and protein concentrations, CD4⁺ T-cell counts, peripheral blood cell counts, and biochemical parameters between the two groups. Between-group comparisons were performed using the Mann–Whitney U test, chi-square test, or Fisher’s exact test, as appropriate. We conducted univariable and multivariable logistic regression analyses to identify factors associated with HIV coinfection. Results The prevalence of HIV coinfection was 44.8%. Compared with patients with neurosyphilis alone, those with HIV coinfection were younger, were more likely to be male, and had higher proportions of a CSF-TRUST titer of 1:1 and higher absolute lymphocyte counts. In contrast, they had lower CD4⁺ T-cell counts and absolute neutrophil counts (all P < 0.001). Multivariable logistic regression analysis showed that increasing age, higher CD4⁺ T-cell counts, and higher absolute neutrophil counts were independently associated with lower odds of HIV coinfection. Male sex, a CSF-TRUST titer of 1:1, and a higher absolute lymphocyte count were independently associated with higher odds of HIV coinfection (all P < 0.01). Conclusions Patients with neurosyphilis and HIV coinfection were characterized by younger age, a marked male predominance, low-titer CSF-TRUST positivity, and alterations in peripheral immune cell profiles. Younger age, male sex, a CSF-TRUST titer of 1:1, lower CD4⁺ T-cell and neutrophil counts, and a higher lymphocyte count were independently associated with HIV coinfection. These findings may facilitate the early identification and risk stratification of HIV coinfection among patients with neurosyphilis.