Response to letter of K. Singh, 'Role of silver nitrate in the efficacy of hydrogen peroxide aerial decontamination systems' regarding S. Ali et al. 'Efficacy of two hydrogen peroxide vapour aerial decontamination systems for enhanced disinfection of meticillin-resistant Staphylococcus aureus, Klebsiella pneumoniae and Clostridium difficile in single isolation rooms'. Issue 3 (November 2017)