It isn't known where this ticket was issued but it was issued to "D V Mason" in February 1917. A "blue ticket" indicated that a soldier had undergone and passed a medical check for venereal disease. Venereal disease was an enormous problem for the New Zealanders serving overseas during World War One. General Alexander Godley wrote to Defense Minister James Allen in 1915, "[r]eally the only trouble I foresee is venereal, I [am] afraid we are bound to lose almost 10% of the men through it. The women here are full of it...."
In the book Johnny Enzed, some research puts the rate of infected men as high as 20%, but a much lower figure is better supported by evidence according to Professor Glyn Harper. Figures given in a 1919 memorandum into the "venereal question" indicate an estimated 6000 men had passed through English V.D. Hospitals and similar numbers had been treated in France, with a smaller but still significant proportion of soldiers treated in Egypt, estimated at around 1000 men. This would put the total number of men in the NZEF infected by venereal disease much nearer to 10% than 20% of the force. The most common diseases were syphilis, gonorrhoea and "soft sore" (a disease that caused genital ulcers).
These diseases were considered very shameful and in the days before antibiotics, the treatment of them was almost uniformly unpleasant and sometimes dangerous. Practical measures of prevention were not widely recommended by the military establishment in the early years of the war. For an interesting history into this issue, read about Ettie Rout - famous now, but infamous at the time, for her work campaigning to institute the wide spread use of prophylactics among soldiers. Her kits were eventually adopted in 1917, but her name was not allowed to be mentioned in connection with their development or implementation in the New Zealand newspapers upon fear of a £100 fine. For more information on the topic of venereal disease in WW1 in general, see Johnny Enzed by Glyn Harper, which gives a very worthwhile overview of the topic from the war's beginning to end and the particular challenges faced in the different locales the NZEF were situated.