To investigate the characteristics of pathogen distribution of community acquired pneumonia (CAP) in elderly patients with diabetes, and to analyze the predictive value of fasting blood glucose (FBG) combined with glycosylated hemoglobin (HbA1c).

Total of 192 elderly patients with diabetes who were discharged from the Fifth People's Hospital of Nanchong from January 2020 to November 2021 were selected by systematic sampling method for cohort study, all of whom were followed up. The incidence of CAP of patients within 3 months after discharge and the distribution characteristics of pathogens were analyzed. All patients were divided into infected group (43 cases) and uninfected group (149 cases) based on whether complicated with CAP, and the levels of FBG and HbA1c between the two groups were compared, respectively. The risk factors of CAP were conducted by multivariate Logistic regression analysis. The predictive values of FBG change rate and HbA1c change rate for concurrent CAP were analyzed by the receiver operating characteristic (ROC) curve, and the predictive performances were evaluated by the area under the curve (AUC).

The incidence rate of CAP was 22.40% (43/192). Among patients with CAP, bacterial infection accounted for the highest proportion (79.07%, 34/43), followed by Mycoplasma pneumoniae infection (4.76%, 2/43), viral infection (4.65%, 2/43), fungal infection (4.65%, 2/43) and bacterial and fungal mixed infection (4.65%, 2/43); Chlamydia pneumoniae infection accounted for the lowest proportion (2.33%, 1/43). After sputum culture, a total of 55 pathogenic bacteria were isolated, among which Gram-negative bacteria, Gram-positive bacteria and fungi accounted for 63.64% (35/43), 27.27% (15/43) and 9.09% (5/43), respectively. The levels of FBG and HbA1c at discharge of patients in infected group were significantly higher than those of 1 month, 2 months and 3 months after discharge (FBG: t = 17.943, 14.535, 16.546; all P < 0.001. HbA1c: t =16.976, 16.735, 16.734; all P < 0.001). And the levels of FBG and HbA1c of Infected patients were significantly higher at above three time points after discharge than those of uninfected patients (FBG: t = 15.435, 46.522, 17.865; all P < 0.001. HbA1c: t = 16.765, 17.057, 16.846; all P < 0.001). The FBG change rate [(48.93 ± 7.61)%] and HbA1c change rate [(65.84 ± 7.97)%] of patients in infected group were significantly higher than those of uninfected group [FBG: (20.04 ± 4.35)%, HbA1c: (34.05 ± 5.11)%], with significant differences (t = 11.026, 15.884; both P < 0.001). Multivariate Logistic regression analysis showed that post stroke dysphagia (OR = 4.246, 95%CI: 1.486-4.264, P < 0.001), concurrent gastroesophageal reflux (OR = 3.888, 95%CI: 1.175-3.946, P = 0.003), FBG change rate at 3 months after discharge (≥ 47.58%) (OR = 4.246, 95%CI: 2.937-5.555, P = 0.015) and HbA1c change rate at 3 months after discharge (≥ 28.65%) (OR = 3.888, 95%CI: 2.689-5.088, P = 0.012) were all influencing factors for CAP. ROC analysis showed that the cut-off values predicted by the change rates of FBG and HbA1c in elderly patients with diabetes complicated with CAP were 47.58% and 28.65%, respectively; and the sensitivity, specificity and AUC were 51.16%, 89.26% and 0.779, 60.47%, 87.92% and 0.741, respectively. The sensitivity, specificity and AUC predicted by the combination of the two indicators were 81.39%, 88.59% and 0.909, respectively, the AUC predicted by the combination of the two indicators were significantly higher than predicted by the change rates of FBG or HbA1c alone, with significant differences (Z = 2.201, P = 0.028; Z = 2.579, P = 0.010).

The incidence of CAP was high in elderly patients with diabetes mellitus, and the Gram-negative bacteria infection was common, the change rate of FBG and HbA1c in infected patients were high, and the combination of the two indicators had a high predictive value for CAP.