This paper aims to investigate the presence of Aggregatibacter actinomycetemcomitans and to assess potential indicators of the risk of severe form(s) of periodontitis. A descriptive cross-sectional study of 156 consecutive patients with periodontitis was conducted. Subgingival plaque samples were collected from the participants. The identification of A. actinomycetemcomitans was performed using quantitative polymerase chain reaction. A descriptive analysis, a chi-square test, and a binary logistic regression statistical evaluation were performed. The prevalence of A. actinomycetemcomitans in this population of 156 participants was 17.30% (27 patients). The prevalence of stage-III periodontitis was 75.6% and greater in older men, while the prevalence of stage-IV periodontitis was 22.4% and greater in younger women. We observed a significant relation between the risk of severe periodontitis (stage-IV) and poor oral hygiene (p = 0.006), attendance at dental appointments (p ≤ 0.001), and familial history of periodontitis (p = 0.032). In conclusion, twenty-seven individuals were positive for A. actinomycetemcomitans. Poor oral hygiene, family history of periodontitis, and irregular attendance at dental appointments were identified as potential risk factors for severe periodontitis in this cohort.