A case-control study of herd- and cow-level risk factors associated with an outbreak of Mycoplasma mastitis in Nemuro, Japan.

The objective of this case-control study was to determine the herd- and cow-level risk factors associated with an outbreak of Mycoplasma bovine mastitis in the winter of 2014-2015 in Nemuro, Hokkaido, Japan. Two questionnaire surveys were sent to all 40 Mycoplasma-infected farms in the area and 73 non-infected farms for the farm-level analysis. Infected cows were matched to twice the number of non-infected cows in the same herds by parity and days after calving. Movement records, dairy herd test records, and clinical records of infected cows and matched non-infected cows were collected for the cow-level analysis. Risk factors for Mycoplasma infection were explored by multivariable analyses at both levels. In the herd-level analysis, tie stall housing for milking cows (odds ratio [OR] = 0.20, 95 % confidence interval [CI]: 0.07-0.60, p =  0.004), consciously wiping of teat openings before milking (OR = 0.15, 95 % CI: 0.02-0.76, p =  0.030), and use of paper towels to wipe teats (OR = 0.31, 95 % CI: 0.09-0.92, p =  0.045) were identified as preventive factors, whereas introduction of cattle (OR = 3.43, 95 % CI: 1.14-10.86, p =  0.030) was identified as a risk factor. In the cow-level analysis, a history of presence in livestock markets (OR = 10.80, 95 % CI: 1.12-104.38, p =  0.040), higher milk yield 2 months prior to Mycoplasma infection (OR = 1.09, 95 % CI: 1.02-1.18, p =  0.014), and previous diagnosis of acute mastitis without isolation of the causal pathogen (OR = 3.14, 95 % CI: 0.86-11.41, p =  0.082) were identified as risk factors. These results highlight the importance of proper milking hygiene control and quarantine of introduced cattle to prevent Mycoplasma infection.