Arthur Middleton died in January 1919, having returned to Australia due to illness in July. The official cause of death was nephritis, a kidney infection, of which a new type was identified during the war. Called trench nephritis, it was diagnosed as coinciding with bronchitis, as opposed to the already understood acute nephritis. That Middleton died of the newly named trench nephritis is suggested by his father, who stated Middleton had been very ill of cold and exposure while fighting with the 42nd Battalion during the German Spring Offensive in the first half of 1918. His medical records also point to a shortness of breath which was a symptom of bronchitis.
Approximately 35,000 British and 200 American soldiers died of trench nephritis, though such mortality rates were considered low. It has been suggested the cause of trench nephritis was rodent-borne hantavirus.
Before the war, Middleton had been a boot maker alongside being a professional soldier who had trained cadets since the start of the war. He also played football with the St Stephens club in the Ipswich and West Moreton competition.
A possibly unrelated Rodney Middleton also played for the club, though he left for Scotland in mid-1914, with only Arthur appearing in subsequent match reports. Arthur Middleton enlisted in March 1917 at his existing rank of Sergeant, though he reverted to Private at his own request following the onset of his illness.
He died on the 23rd of January at the Camp Clearing Hospital in Enoggera, Brisbane with his mother by his side, and was buried with full military honours.