Impact of insulin storage and syringe reuse on insulin sterility in diabetes mellitus patients in Mwanza Tanzania

This study evaluated microbial contamination in insulin products used by diabetic patients in Mwanza, Tanzania, focusing on syringe reuse and improper storage practices, such as using clay pots or charcoal and water buckets. Conducted in 2024, this cross-sectional, laboratory-based study collected 81 insulin vials from 51 diabetic patients at Bugando Medical Centre through appointments and home visits. The insulin samples were cultured for microbial growth, and bacteria were identified using in-house biochemical tests. The median age of the patients was 50 [IQR: 25-64] years; half had diabetes mellitus for six years and used insulin for five years. Half were male, 52% had primary education, and 49% stored insulin in clay pots. Out of 81 insulin samples collected from diabetic patients, 5 (6.2%) showed microbial contamination, mainly due to Gram-positive bacteria. Contaminated products included Humulin R, Humulin N, and Biosulin 30/70. Storage in clay pots had higher contamination (16%) than storage in refrigerators (0%). Improper storage practices, such as immersing vials in water or a mixture of water and sand within clay pots expose insulin to microbial contamination, which increases the risk of infections. To ensure safety and effectiveness patients should be educated to follow the manufacturer's storage guidelines.