In 1886, Niven left private practice after four years and was appointed as Medical Officer of Health for Oldham, a post that he held until 1894. He was simultaneously appointed as Medical Superintendent at Westhulme Hospital. During that time, he campaigned to have tuberculosis classed as a notifiable disease by the town's council, obtaining the support of local medical practitioners but failing in his pioneering aim. Doctors and physicians in Oldham raised enough money to send Niven to Berlin to study with Robert Koch, who had discovered the TB bacillus in 1882, thereby proving that the disease was not caused by "bad air" as was generally believed in accordance with the prevalent miasma theory. He also used Koch's treatment at the Oldham General Infirmary on his return, as well as dealing with smallpox, typhus, measles, scarlet fever and whooping cough. An Oldham Chronicle obituary of 1925 said: "Dr Niven also showed an interest in child welfare well in advance of his time."
