Ceftriaxone and Azithromycin Minimum Inhibitory Concentration of Salmonella Typhi and Paratyphi A Blood Isolates of Children with Enteric Fever

Objectives: Enteric fever caused by Salmonella Typhi and Paratyphi is endemic in India. Ceftriaxone and azithromycin are commonly used to treat enteric fever, but resistance to these antibiotics is emerging. The study was done to determine the ceftriaxone and azithromycin minimum inhibitory concentration (MIC) of S . Typhi and Salmonella Paratyphi A isolated from the blood of pediatric enteric fever patients. Material and Methods: Isolate of S . Typhi and Paratyphi A from the blood of pediatric patients with enteric fever at Kanchi Kamakoti CHILDS Trust Hospital from September 2023 to June 2024 were tested for ceftriaxone and azithromycin MIC through the Epsilometer test. Results: 150 Salmonella (124 S . Typhi and 26 Salmonella Paratyphi A) isolates were included in this study. All Salmonella isolates were sensitive to ceftriaxone. The mean ceftriaxone MIC of S . Typhi was 0.108 µg/mL [95% confidence interval (CI): 0.101–0.114], and that of Salmonella Paratyphi A was 0.140 µg/mL (95% CI: 0.123–0.157). All the S . Typhi isolates were sensitive to azithromycin, and the mean azithromycin MIC for S .Typhi was 6.62 µg/mL (95% CI: 5.99–7.25). Salmonella Paratyphi A showed a statistically significantly higher mean MIC for both ceftriaxone (difference of 0.032 µg/mL, P = 0.001) and azithromycin (difference of 4.61 µg/mL, P = 0.000). Conclusion: All S . Typhi and S Paratyphi A, in our study, were sensitive to ceftriaxone, and their mean MIC was well below the sensitive breakpoint (≤1 µg/mL). All the S . Typhi isolates were sensitive to azithromycin with a mean MIC much below the sensitive breakpoint of ≤16 µg/mL. S . Paratyphi A showed a statistically significant higher mean MIC for both ceftriaxone and azithromycin than S . Typhi.