COVID‑19 has imposed an extraordinary global burden, resulting in more than six million deaths and over five hundred million infections worldwide ⁽¹⁾. The pandemic has not only strained healthcare systems but also reshaped public health priorities, with successive variants such as Delta and Omicron intensifying the challenge.

Initial clinical observations from Wuhan revealed the wide spectrum of COVID‑19 manifestations, ranging from mild respiratory illness to severe pneumonia and multi‑organ dysfunction ⁽²⁾. These early reports underscored the unpredictable nature of the disease and the necessity for vigilant monitoring of hospitalized patients.

Subsequent analyses identified comorbidities as critical determinants of outcome, with evidence showing that conditions such as diabetes and hypertension were strongly associated with increased mortality among inpatients ⁽³⁾. Large‑scale epidemiological data further confirmed that underlying health conditions were common and often influenced disease severity, highlighting the need for comorbidity‑specific risk assessment ⁽⁴⁾.

Cardiovascular involvement has also been emphasized, with systematic reviews documenting myocarditis and hypertension as frequent comorbidities in COVID‑19 patients, suggesting a potential role in disease progression and adverse outcomes ⁽⁵⁾. Neurological and autoimmune conditions have likewise been examined, with reports of myasthenia gravis patients experiencing variable outcomes depending on respiratory involvement and immunosuppressive therapy, illustrating the complexity of autoimmune interactions with COVID‑19 ⁽⁶⁾.

Immunocompromised populations have drawn particular attention. Reviews of patients living with HIV indicate that while infection rates may be comparable to the general population, many studies suggest a heightened risk of severe prognosis, reinforcing the importance of tailored management strategies ⁽⁷⁾. Similarly, investigations into advanced liver disease have shown that although susceptibility to infection may be increased, outcomes are not uniformly poor, pointing to heterogeneity in comorbidity effects ⁽⁸⁾.

Among all comorbidities, diabetes mellitus has consistently emerged as one of the most prevalent and impactful in COVID‑19 cohorts worldwide ⁽⁹⁾. Hyperglycemia, immune dysregulation, and heightened inflammatory responses are thought to contribute to poorer outcomes, whereas hypertension, though common, has demonstrated variable associations with severity, possibly influenced by treatment regimens and underlying cardiovascular risk.

Taken together, these findings highlight the necessity of understanding the independent impact of specific comorbidities on COVID‑19 prognosis. The present study was therefore designed to compare outcomes in patients with exclusive comorbidities — type 2 diabetes mellitus, hypertension, or autoimmune disease — against those without comorbidities, thereby providing clearer insights into risk stratification and clinical management.

This investigation was conducted as a retrospective comparative study at Bowring and Lady Curzon Hospital, Bengaluru, spanning the period from October 2020 to February 2022. The study population comprised 224 patients aged between 18 and 60 years who had tested positive for COVID 19 and were admitted to the hospital. To ensure clarity in assessing the impact of individual comorbidities, only patients with a single comorbidity were included, specifically those with type 2 diabetes mellitus, hypertension, or autoimmune disease. Patients without any comorbidities served as the control group. Individuals with multiple comorbidities and pregnant women were excluded to minimize confounding factors. Clinical records were reviewed to extract demographic details, duration of hospital stay, and clinical outcomes, defined as discharge or death. Patients were categorized into five groups: those with diabetes mellitus, hypertension, autoimmune disease, HIV/AIDS, and those without comorbidities. The primary outcomes of interest were mortality and mean duration of hospitalization, which were compared across groups. Data compilation and statistical analysis were performed using Microsoft Excel 2019. The chi square test was applied to assess categorical differences in mortality, while the z test for two samples with means was used to evaluate differences in hospital stay duration. A p value of less than 0.05 was considered statistically significant. Ethical clearance for the study was obtained from the Institutional Ethics Committee of Bowring and Lady Curzon Medical College and Research Institute prior to data collection. Patient confidentiality was maintained throughout, with all records anonymized before analysis. The study adhered to institutional and international ethical standards for retrospective research.

A total of 224 patients admitted with COVID‑19 between March 2020 and March 2022 were included in the study. Patients were categorized into five groups based on comorbidity status: Group A comprised individuals with HIV/AIDS (n = 5), Group B included those with diabetes mellitus (n = 80), Group C consisted of patients with hypertension (n = 60), Group D represented those with autoimmune disease (n = 5), and Group E served as the control group with no comorbidities (n = 74).

Results are further tabulated below:

Table 1- Mortality outcomes by Co-morbidity.

Table 2 – Comparative outcomes Summary

As shown in Table 1, mortality was significantly higher among patients with diabetes mellitus (60%) compared to controls (12.5%, p = 0.0003). Hypertension (25%) and autoimmune disease (40%) showed numerically increased mortality but did not reach statistical significance (p = 0.06 and p = 0.09, respectively). HIV/AIDS patients demonstrated a mortality rate of 40%, similar to autoimmune disease, but statistical significance was not achieved (p = 0.11)

The mean duration of hospital stay across groups is summarized in Table 2. The mean duration of hospital stay was longest among hypertensive patients (11.88 ± 16.16 days) and shortest among autoimmune disease patients (5.2 ± 3.54 days). HIV/AIDS patients had an average stay of 7.4 ± 3.2 days, which was comparable to controls (9.28 ± 4.0 days). Differences across groups were not statistically significant.

Overall, diabetes mellitus emerged as the only comorbidity significantly associated with increased mortality. HIV/AIDS and autoimmune disease showed higher mortality trends but were limited by small sample sizes. Hospital stay duration did not differ significantly across groups.

The above figure visually depict the comparative outcomes among the five comorbidity groups.

The present study demonstrates that type 2 diabetes mellitus was significantly associated with poorer outcomes in COVID 19 patients, with mortality rates far exceeding those of non comorbid controls. This finding aligns with the broader literature, which has consistently identified diabetes as an independent predictor of adverse prognosis. Hyperglycemia, immune dysregulation, and heightened inflammatory responses are thought to underlie this vulnerability, contributing to impaired viral clearance and increased susceptibility to severe disease (9). Although hypertension, autoimmune disease and HIV/AIDS groups exhibited numerically higher mortality, statistical significance was not achieved in this cohort. This may be attributable to the relatively small sample size, particularly in the autoimmune group, and the heterogeneity of disease expression. Previous reports have highlighted similar variability. For example, patients with myasthenia gravis infected with COVID 19 demonstrated a wide range of outcomes, with some requiring mechanical ventilation while others recovered without respiratory support, underscoring the complex interplay between immunosuppressive therapy and viral pathogenesis (6). Immunocompromised populations such as those living with HIV have also been studied extensively. Reviews of clinical outcomes suggest that while infection rates may be comparable to the general population, many studies indicate a heightened risk of severe prognosis, reinforcing the need for tailored management strategies in these patients (7). Likewise, patients with advanced liver disease have been shown to be more susceptible to COVID 19, yet outcomes are not uniformly poor, illustrating that not all comorbidities exert the same influence on prognosis (8). The strong association between diabetes and mortality observed in this study is consistent with case reports and systematic reviews that have documented worsening outcomes in diabetic patients, even when disease onset was precipitated by COVID 19 itself (9). Furthermore, systematic reviews of HIV positive cohorts have reported high rates of hospitalization and intensive care admission, with mortality approaching 14 %, again emphasizing the role of immune compromise in shaping prognosis (10). Neurological comorbidities have also been highlighted in the literature. Case reports of patients with myasthenia gravis describe exacerbations of respiratory dysfunction following COVID 19 infection, though outcomes varied, with some patients recovering favorably despite initial deterioration (11). Larger case series have confirmed this variability, noting that while some patients required mechanical ventilation, others responded to oxygen therapy alone, suggesting that immunosuppressive medication does not invariably worsen outcomes (12). Taken together, these findings reinforce the conclusion that diabetes mellitus exerts a uniquely deleterious effect on COVID 19 prognosis, while hypertension and autoimmune conditions demonstrate more heterogeneous associations. The variability observed across comorbid groups underscores the importance of larger, multicentric studies to delineate the independent contributions of each condition. Our results add to the growing body of evidence that comorbidity specific risk stratification is essential for optimizing patient management and resource allocation during pandemics. Limitations This study, while offering valuable insights into the impact of comorbidities on COVID 19 prognosis, has several limitations. First, the retrospective design restricted control over confounding variables, as data were derived from hospital records rather than prospectively collected, potentially introducing documentation bias. Second, being conducted at a single tertiary care center limits generalizability to broader populations with different demographic and healthcare characteristics. Third, the sample size for certain comorbidity groups, particularly autoimmune disease and HIV/AIDS, was small, reducing statistical power and increasing the likelihood of type II error. Despite these limitations, the study provides preliminary evidence that diabetes mellitus exerts a uniquely deleterious effect on COVID 19 outcomes, while hypertension, autoimmune disease, and HIV/AIDS demonstrate more heterogeneous associations. Future multicentric, prospective studies with larger sample sizes and comprehensive clinical data are warranted to validate and extend these findings.

This comparative study highlights the significant impact of type 2 diabetes mellitus on COVID‑19 prognosis, with mortality rates markedly higher than those observed in non‑comorbid patients. In contrast, hypertension, autoimmune disease, and HIV/AIDS demonstrated numerically increased mortality but without statistical significance, reflecting the heterogeneity of their influence and the limitations of small subgroup sizes. Importantly, the duration of hospital stay did not differ significantly across groups, suggesting that mortality risk may be driven more by underlying metabolic and immunological factors than by length of hospitalization.

Taken together, these findings reinforce the importance of comorbidity‑specific risk stratification in the management of COVID‑19. Diabetes mellitus emerges as a critical determinant of poor outcome, warranting heightened vigilance and tailored therapeutic strategies in affected patients. Future multicentric, prospective studies with larger sample sizes and more detailed clinical data are essential to clarify the independent contributions of hypertension, autoimmune disease, HIV/AIDS, and other comorbidities to COVID‑19 prognosis.

Acknowledgement

The authors express their sincere gratitude to the Bowring and Lady Curzon Medical College and Research Institute for granting ethical clearance and providing access to hospital records essential for this study. We are indebted to the medical and administrative staff of Bowring and Lady Curzon Hospital for their support in data collection and patient record management during the study period. We also acknowledge the guidance and encouragement received from our colleagues at Sri Atal Bihari Vajpayee Medical College and Research Institute, whose insights greatly enriched the research process.