Diabetes and respiratory diseases as comorbid conditions in COVID-19 patients from Kazakhstan: a retrospective pilot study

Introduction

The recent COVID-19 pandemic raised significant concerns about health care outcomes of individuals diagnosed with COVID-19 infection experiencing comorbid conditions, particularly respiratory diseases, such as chronic bronchitis and pneumonia (Pya et al., 2021). In 2017, an estimated 544.9 million people worldwide were living with chronic respiratory diseases (CRDs)—a 39.8% increase since 1990 (Soriano et al., 2020). Using Global Burden of Disease Study (GBD) 2019 estimates, CRDs ranked as the third-leading cause of death globally; however, according to WHO Global Health Estimates for 2021, ischemic heart disease was the leading cause, COVID-19 ranked second, stroke third, and chronic obstructive pulmonary disease fourth (Momtazmanesh et al., 2023; Otegenova et al., 2024).

Chronic bronchitis, one of the most common respiratory diseases, is of particular concern due to its association with severe respiratory complications, especially in the context of COVID-19. COVID-19 frequently leads to pneumonia, significantly worsening outcomes for patients with pre-existing respiratory diseases, such as chronic bronchitis. These patients often require hospitalization, intensive care, and long-term management of complications, such as interstitial lung diseases and pulmonary vascular disease (Gülsen et al., 2021; Iskakova et al., 2023).

Low and middle-income countries bear a heavy burden of respiratory diseases and multimorbidity, placing a tremendous strain on healthcare systems (Abebe et al., 2020; George et al., 2020). The global burden of chronic diseases, particularly respiratory diseases, has been steadily increasing over the past few decades. These diseases not only lead to significant morbidity and mortality but also lead to increasing healthcare systems burden worldwide (Patterson et al., 2009). It is predicted that by 2035, the number of people suffering from diabetes could rise to 592 million, particularly in low and middle-income countries (Divers et al., 2020). The presence of both diabetes and respiratory diseases in a single patient significantly increases the risk of severe COVID-19 progression and mortality (Liu et al., 2020). These comorbid conditions exacerbate adverse health events, leading to a deterioration in the patient’s overall condition (Gold et al., 2020).

Global data indicated a decline in the mortality rate from chronic respiratory diseases by 2.41% annually between 1990 and 2017. However, regions with low social-demographic indices continue to exhibit high mortality rates from respiratory diseases, suggesting the need to address preventable causes of mortality in countries like Kazakhstan (Kosherbayeva et al., 2024).

Kazakhstan, like many other countries, faces challenges associated with an aging population, which has led to an increase in the prevalence of chronic diseases, including chronic bronchitis. Smoking, air pollution, and occupational exposures are significant risk factors contributing to the high prevalence of respiratory diseases in Kazakhstan. While the mortality rate from lower respiratory infections has been declining since 1991, there has been a notable rise in respiratory-related deaths among older age groups, exacerbated by limited healthcare resources (Supiyev, 2018; Otegenova et al., 2024). Due to the potential underreporting of COVID-19 cases, conducting studies on the interrelationship between COVID-19 and other respiratory infections is challenging (Rezaei, 2024).

The prevalence of chronic bronchitis and its co-occurrence with COVID-19 in Kazakhstan remains underreported, though early data suggest these comorbidities are linked to higher mortality rates and more severe clinical outcomes (Chen et al., 2023). Unlike asthma, which has shown no consistent association with severe COVID-19 progression, chronic bronchitis poses a significant risk, emphasizing the need for focused prevention and treatment strategies (Dyusupova et al., 2021).

Patients with respiratory diseases, particularly chronic bronchitis, should be classified as a high-risk group and receive appropriate treatment and monitoring. This includes regular lung function assessments, early interventions to address symptom exacerbations, and robust infection prevention measures (Sanyaolu et al., 2020; Marron et al., 2021). Ensuring access to medical resources for treating COVID-19 and its complications is equally critical (Cheng et al., 2021). Special attention should be given to infection prevention in patients with chronic respiratory diseases, as well as ensuring access to essential medical resources for the treatment of COVID-19 and its complications (Mahumud, Kamara & Renzaho, 2020).

The increasing burden of diabetes and chronic respiratory diseases among COVID-19 patients is not unique to Kazakhstan but reflects a broader global trend, particularly in low- and middle-income countries (LMICs). Understanding the interplay of these comorbidities is critical for developing targeted public health interventions applicable both regionally and internationally.

Thus, the aim of this study is to analyze trends in the prevalence of diabetes and respiratory diseases as comorbidities in patients presenting with recent COVID-19 infections, based on the information obtained from several clinics in Almaty, Kazakhstan. We aimed to look at the burden of these conditions by age groups using medical record review approaches, testing of biological samples, and evaluating data using existing medical records. Our ultimate aim is to provide policy recommendations for the reduction of comorbidity burden and improving primary prevention activities in Kazakhstan and Central Asia.

Materials & Methods

Sampling and participants

We recruited a sample of 292 research participants from a total of 524 potentially eligible patients monitored in clinics and regional hospitals in Almaty. The sample size was determined using Epi Info, a statistical software developed by the Centers or Disease Control and Prevention (CDC) (Division of Health Informatics & Surveillance (DHIS), Center for Surveillance, Epidemiology & Laboratory Services (CSELS), 2020). We retrospectively reviewed electronic medical records (EMRs) of patients hospitalized with laboratory-confirmed COVID-19 in Almaty, Kazakhstan. The catchment population of the participating institutions was approximately 150,000 residents at the time of the study. From EMRs, 524 records were identified as potentially eligible. After screening, 232 cases were excluded due to incomplete records (n = 124), not meeting inclusion criteria or having unrelated comorbidities (n = 68), or missing key outcome variables (n = 40). The final sample comprised 292 patients.

All included patients had at least one documented comorbid condition (diabetes mellitus, pneumonia, or chronic bronchitis). Consequently, our comparisons are performed across comorbidity subgroups rather than against a non-comorbid control group. The flow of participants is presented in Fig. 1.

Results

The study included 292 patients with a mean age of 55 years (range 18–91 years), of whom 104 (35.7%) were male. The study sample predominantly consisted of younger to middle-aged adults, with the majority falling into the 18–44 years age group (41.1%), followed by those aged 45–60 years (31.5%), and the remaining >60 years group representing 27.4% of the total. Among the total population with confirmed COVID-19, the most common comorbid conditions were pneumonia and chronic bronchitis. Pneumonia was present in 166 (56.8%) of the participants, while chronic bronchitis affected 126 (43.2%). Pneumonia had the highest prevalence in the 45–60 years age group, accounting for 46.7% of participants with this condition. Chronic bronchitis was most prevalent in the same age group, with 42.1% of participants affected, followed by 24.6% in the 18–44 years age group and 29.4% in those aged over 60 years. Table 1 outlines basic clinical characteristics of the study participants. It illustrates the demographic and clinical outcomes, including mortality (Death), clinical improvement (Improvement), change in condition (No Change), and the need for artificial ventilation (Artificial Ventilation). Specifically, 27% of patients died in the hospital due to complications. For each outcome, the number of patients (N), percentage (%), and p-values are presented, highlighting the statistical significance of each observation.

Table 2 provides insights into the adjusted odds ratios (AORs) and 95% confidence intervals (CIs) for clinical outcomes in COVID-19 patients based on demographic characteristics (age and gender) and comorbidities (pneumonia and chronic bronchitis). The outcomes analyzed include Death, Improvement, No Change, and the Need for Artificial Ventilation.

Older patients were at a much higher risk of experiencing severe outcomes. Those aged 45–60 years had 1.6 times higher odds of dying compared to younger adults (18–44 years), while patients over 60 years had more than double the risk (2.4 times higher). On the other hand, the odds of improvement decreased significantly with age, and patients over 60 had the lowest odds of recovery. The need for artificial ventilation was especially high in the oldest age group, with the odds being three times greater than for younger adults. Male patients were at greater risk of adverse outcomes compared to females. They were 1.5 times more likely to die and 1.6 times more likely to require artificial ventilation. However, their odds of improvement were slightly lower than for females. Pneumonia had a strong negative impact on outcomes. Patients with pneumonia were 1.8 times more likely to die and 2.2 times more likely to need artificial ventilation compared to those without pneumonia. Their chances of improvement were also significantly lower. Chronic bronchitis also posed risks but to a lesser extent than pneumonia. It increased the odds of death and the need for ventilation, although its impact on improvement was less severe. This table highlights the critical role that age, gender, and comorbidities play in determining outcomes for COVID-19 patients.

Diabetes was independently associated with all adverse COVID-19 outcomes. Patients with diabetes had 1.7 times higher odds of death (95% CI [1.3–2.2]) and more than twice the odds of requiring mechanical ventilation (AOR: 2.1, 95% CI [1.6–2.7]). Their likelihood of clinical improvement was significantly lower (AOR: 0.7, 95% CI [0.5–0.9]), and they were more likely to experience no change in condition (AOR: 1.4, 95% CI [1.1–1.8]). These results underscore the central role of diabetes in worsening COVID-19 prognosis, independent of other comorbidities.

Table 3 compares the clinical outcomes of COVID-19 patients with diabetes who also have either chronic bronchitis or pneumonia as a comorbidity. The outcomes investigated include Death, Improvement, No Change, and Transition to Artificial Ventilation, expressed as percentages, along with odds ratios (OR) and 95% confidence intervals.

Patients with chronic bronchitis exhibited elevated risks across several outcomes. The odds of death were significantly higher (OR: 1.4, 95% CI [1.1–1.8]), while the likelihood of improvement was slightly reduced (OR: 0.9, 95% CI [0.7–1.2]). Additionally, the odds of experiencing no change in clinical condition were increased (OR: 1.5, 95% CI [1.2–2.0]), and the need for artificial ventilation was significantly higher (OR: 1.8, 95% CI [1.4–2.3]).

Patients with pneumonia faced even worse outcomes, with significantly higher odds of death (OR: 1.8, 95% CI [1.4–2.3]) and artificial ventilation (OR: 2.2, 95% CI [1.7–2.9]). Improvement rates were substantially lower in pneumonia patients (OR: 0.6, 95% CI [0.4–0.8]), while the odds of no change were also elevated (OR: 1.7, 95% CI [1.3–2.2]). These findings were supported by chi-square tests, revealing statistically significant associations across all clinical outcomes (p < 0.05).

Mortality was notably higher among patients with pneumonia (16.8%) compared to those with chronic bronchitis (10.6%), with a p-value of 0.005. Improvement rates were greater in the chronic bronchitis group (18.2%) than in the pneumonia group (9.9%), p = 0.03. Similarly, the need for artificial ventilation was more frequent in pneumonia cases (19.9%) than in chronic bronchitis cases (11.3%), p = 0.001.

These findings highlight the heightened risks associated with chronic bronchitis and pneumonia in COVID-19 patients with diabetes, emphasizing the need for targeted interventions and close monitoring of these high-risk groups.

Discussion

Our key finding is that higher mortality and ventilation rates for COVID-19 patients were observed in those with confirmed pneumonia. We also observed very high COVID-19 mortality rate among pneumonia patients in comparison to other middle income countries (Khedr et al., 2022), with studies indicating that the prevalence of severe respiratory complications and secondary bacterial infections significantly contributes to this outcome. As this group of patients exhibited an alarmingly high mortality rate, particularly among those with severe comorbid conditions, there is a critical need to explore the critical impact of comorbidities on COVID-19 outcomes.

Our revised analysis confirms that diabetes is a significant independent risk factor for adverse COVID-19 outcomes in hospitalized patients. Patients with diabetes had substantially higher odds of death and the need for mechanical ventilation, even after controlling for age, gender, and other respiratory comorbidities. These findings are consistent with global studies showing that hyperglycemia and insulin resistance contribute to immune dysregulation, delayed viral clearance, and increased inflammatory response in COVID-19 patients (Cheng et al., 2021; Chen et al., 2023; Gazezova et al., 2023).

The inclusion of diabetes in all multivariable models strengthens the coherence between our research question and statistical approach. In contrast to chronic bronchitis, which showed a moderate association with poor outcomes, diabetes had a more consistent and pronounced impact across all outcome domains. Pneumonia remained the strongest respiratory predictor of death, but diabetes emerged as a parallel driver of severity, especially among middle-aged and older adults. This dual burden reflects the reality in Kazakhstan, where the prevalence of type 2 diabetes is rising and often coexists with underdiagnosed respiratory conditions (Soriano et al., 2020; Kosherbayeva et al., 2024).

The combination of diabetes and pneumonia significantly amplified clinical risk, suggesting synergistic interactions between metabolic and respiratory pathways. These data support targeted early intervention and multidisciplinary management strategies in COVID-19 patients with chronic conditions. Importantly, our findings also highlight the need for improved glycemic control protocols in inpatient COVID-19 care, especially in middle-income countries facing dual challenges of noncommunicable and infectious disease burdens.

Previously published research from Kazakhstan highlighted that pneumonia remains a leading cause of hospitalization and death, particularly in older adults with comorbid conditions such as diabetes and chronic respiratory diseases. According to Zhussupov et al. (2021) pneumonia cases during the COVID-19 pandemic in Kazakhstan were characterized by delayed hospital admissions, limited access to critical care resources, and high prevalence of multidrug-resistant bacterial infections, all of which compounded mortality risks (Smagul et al., 2022). The increased mortality in pneumonia cases can also be attributed to Kazakhstan’s environmental and healthcare challenges. Studies by Kerimray et al. (2020) emphasize that high levels of air pollution, including particulate matter in urban centers like Almaty, contribute to a higher baseline prevalence of chronic respiratory diseases, which exacerbate the progression of pneumonia in COVID-19 patients. Furthermore, smoking prevalence, reported to be over 25% among adults in Kazakhstan, has been strongly linked to both chronic bronchitis and pneumonia, compounding the severity of respiratory infections (Kazakhstan, Office for Prevention & Control of NCDs (MOS), Tobacco (TOB), WHO Europe, 2019).

Our findings, coupled with published studies, suggest that pneumonia substantially increases the risk of severe respiratory failure requiring mechanical support. In this study, pneumonia is linked to higher mortality, a greater need for mechanical ventilation, and less improvement compared to chronic bronchitis. These statistically significant differences emphasize the importance of tailored clinical strategies based on whether patients have chronic bronchitis or pneumonia as a comorbidity with COVID-19 and diabetes.

The findings of this study also provide valuable insights into the clinical outcomes of COVID-19 patients with diabetes. The most substantial impact of these conditions was observed in the 45–60 years age group, indicating that middle-aged adults with these comorbidities may experience more severe clinical outcomes. It reinforces the need to focus care and resources on older adults, male patients, and those with pneumonia or chronic bronchitis to improve their chances of recovery.

This trend is consistent with other studies conducted in Kazakhstan that highlight the high prevalence of COVID-19 and associated complications among older male populations (Yegorov et al., 2021; Zhussupov et al., 2021). Previous research in Central Asia has also shown that older adults, especially males, have higher rates of diabetes and respiratory illnesses, leading to more severe COVID-19 outcomes (Almagro et al., 2020; Steinthorsdottir et al., 2020). This pattern emphasizes the need for targeted healthcare strategies to manage these comorbidities effectively, particularly among middle-aged COVID-19 patients.

The prevalence of pneumonia and chronic bronchitis observed in this study reflects the broader disease trends within Kazakhstan. Chronic respiratory diseases are widespread, partly due to high smoking rates and environmental factors such as air pollution, which are especially prominent in industrialized regions like Almaty (Kerimray et al., 2020). These factors contribute to the higher rates of chronic bronchitis found among middle-aged and older adults.

Our analysis shows a statistically significant difference in clinical outcomes between patients with chronic bronchitis and those with pneumonia. Specifically, among COVID-19 patients with diabetes, those with pneumonia had higher mortality rates and a greater need for artificial ventilation compared to those with chronic bronchitis, indicating that pneumonia poses a greater risk in this patient population. This finding aligns with global studies indicating that pneumonia, particularly bacterial pneumonia as a secondary infection, significantly worsens COVID-19 prognosis (WHO, 2021; Scott et al., 2022). Kazakhstan has reported challenges in managing COVID-19 complications, especially in patients with comorbidities such as diabetes (Gazezova et al., 2023). The healthcare system in Kazakhstan, while rapidly developing, faces resource limitations that affect the management of severe respiratory conditions. This is evident in the higher need for artificial ventilation in pneumonia patients, suggesting that pneumonia presents a critical challenge that requires targeted healthcare strategies, such as early intervention protocols and enhanced monitoring in diabetic patients.

The improvement rate among chronic bronchitis patients (18.2%) compared to pneumonia patients (9.9%) suggests that chronic bronchitis, despite being a long-term condition, may allow for better management outcomes when compared to the acute onset of pneumonia. This finding is in line with studies from other regions showing that chronic bronchitis patients, when managed with bronchodilators and steroids, can achieve good outcomes even when infected with COVID-19 (Bai et al., 2022). However, the higher mortality and ventilation rates among pneumonia patients reflect Kazakhstan’s broader need to enhance its critical care capacity, particularly for respiratory diseases. Pneumonia remains a leading cause of hospital admissions and mortality in the country, highlighting the urgency for improved diagnostic capabilities and access to ventilators (Vinnikov et al., 2023).

Our findings align with global research showing that diabetes and chronic respiratory conditions significantly worsen COVID-19 outcomes. Similar trends have been observed in other middle-income countries, including Brazil, India, and South Africa, where high rates of air pollution and smoking exacerbate respiratory disease prevalence. These results suggest that public health interventions targeting multimorbidity in COVID-19 patients should be prioritized not only in Kazakhstan but also in other LMICs facing similar epidemiological challenges.

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