Money and Microbes: A Global Systematic Review and Meta-Analysis of Currency Contamination

Money passes through numerous hands daily, creating an ideal medium for the accumulation and transfer of pathogenic microorganisms. Despite this, a comprehensive synthesis of contamination levels on currency is lacking.

This systematic review and meta-analysis assessed the prevalence and types of microbial contamination on money.

A systematic search was conducted for studies published up to December 2024. The review followed the PRISMA guidelines. Pooled prevalence estimates were calculated via a random-effects model. Heterogeneity between studies was assessed via the I² statistic, and sensitivity analyses were performed.

A total of 35 studies met the eligibility criteria. The overall pooled prevalence of microbial contamination on money was 12.8% (95% CI: 10.9-14.7). Subgroup analyses revealed pooled prevalence rates of 14.0% (95% CI: 11.1-16.8) for bacteria, 17.0% (95% CI: 12.1-21.8) for fungi, and 9.7% (95% CI: 6.8-12.7) for parasites. Klebsiella spp. 20.3% (95,% CI: 10.4-30.2) and Staphylococcus aureus 19.8% (95% CI: 12.7-26.8) were the predominant bacterial isolates, whereas Aspergillus niger 42.2% (95% CI: 29.1-55.3) was the most frequently identified fungal species, and Entamoeba histolytica was the most frequently identified parasites 18.9% (95% CI: 1.3-36.5). Contamination was greater for paper money 21.3% (95% CI: 13-29.6) than for coins 14.8% (95% CI: 4.3-25.3). Specifically, bacteria were more common on coins 26.4% (95% CI: 8.6-44.2) than on paper money 23.7% (95% CI: 9.5-37.8), whereas parasites were more common on paper money 18.1% (95% CI: 1.2-15.4) than on coins 2.1% (95%, CI: 1.2-3.0). The microbial load of the dirty notes was more 3.0% (95% CI: 2.3-4.1) and that of the newer notes was 2.2% (95% CI: 1.3-3.7).

Money is consistently contaminated with potentially pathogenic microbes. Although direct transmission has not been definitively proven, the frequent presence of clinically significant microorganisms on money poses a credible public health risk.