Increasingly there is demand for data which directly quantifies the impact of hygiene interventions on infection rates. In the domestic setting, where infection transmission involves a complex web of inter-related pathways, this makes it impossible to quantify relative risks from individual critical control points such as high frequency contact surfaces and cloths. In recent years, Professor Gerba, Dr Chaidez and colleagues have developed Quantitative Microbial Risk Assessment methods to make direct estimates of the impact of domestic hygiene procedures such as hand and laundry hygiene on infection rates.
This latest study, carried out in urban Mexican homes, evaluates infection risks due to hand to mouth exposure to Salmonella sp. in kitchen cleaning clothes using a dynamic exposure model. Occurrence of Salmonella was studied in clothes taken from 60 homes over 6-weeks, in which half disinfected clothes with a sodium hypochlorite based disinfectant cleaner. Overall, Salmonella was absent in 1.1% and 3.89% of test and control group households, respectively, with bacterial counts up to 105 (MPN) in control clothes and 103 in treated clothes.
Using published data on Salmonella transfer rates from clothes to hands and hand to lips, surface touch rates, infectious doses etc, it was calculated, using standard QMRA methods, that yearly risks of infection for the kitchen cleaning clothes for the control group ranged from 0.0023 to 0.096 depending on the number of surfaces touched before touching the mouth. This is higher than guidance on acceptable risk of waterborne Salmonella infection, defined as 1:10,000 (0.0001) per year. In the USA States, the yearly risk of illness from Salmonella is estimated at 0.0045. A reduction greater than 98% of the probability of Salmonella infection was observed between cleaning cloths used by non disinfectant users and disinfectant users under all scenarios of number of clean surfaces touched on yearly basis. The authors conclude that the risks of infection could be further reduced by developing more effective procedures for reducing Salmonella in cleaning clothes.
The study can be found in Letters in Applied Microbiology 2014;59: 487-492
