Risk-based control of Campylobacter spp. in broiler farms and slaughtered flocks to mitigate risk of human campylobacteriosis – A One Health approach

Effects of risk-based control of Campylobacter spp. in Danish broiler farms and flocks were simulated, to assess potential reductions of human risk of campylobacteriosis, associated to the consumption of poultry meat produced in Denmark. Two national data streams were used and represented: Flock status by testing cloacal swabs (CS, 2018–2019) and carcass status by testing leg skin samples (LS, 2019). In the CS surveillance component all flocks slaughtered at the two major Danish slaughterhouses were tested with a polymerase chain reaction (PCR), while in LS one third randomly selected flocks were tested by culture (results in colony forming units per gram, cfu/g). Each farm was identified by its Central Husbandry Register (CHR) number. Two risk farm classification strategies (I-II) were based on CS data from 2018. Farms were classified as: always negative (Neg-CHRs), low risk (LowR-CHRs) and high risk (HighR-CHRs) farms. In strategy I, HighR-CHRs had more than five positive flocks, while in strategy II; they had more than 27.8% of the slaughtered flocks positive. Those two cut-offs were the annual 3^rd quartiles across positive farms. Thereafter, a risk assessment model was used to estimate the annual relative risk (RR) of human campylobacteriosis in 2019, compared to that of 2013. Three hypothetical levels of cfu/g reductions (A, B and C) were simulated on the LS positive flocks (> 10 cfu/g) slaughtered by HighR-CHRs and were pairwise combined with the two classification strategies, yielding six risk-mitigation scenarios (A I-II; B I-II; C I-II). In scenarios A I-II, zero cfu/g were simulated, while in scenarios B and C, the original cfu/g were divided by three and by two. For each scenario, RRs were compared to the RR of the original cfu/g (scenario O).

In 2018, if all flocks from HighR-CHRs had been negative, the annual CS flock prevalence would have reduced from 19.7% to 7.6% (strategy I) or 9.6% (strategy II). Whereas in 2019, it would have reduced from 17.1% to 7.8% or 11.6%. In both years, HighR-CHRs delivered a high percentage of the total annual positive flocks (61.4–54.4% under strategy I and 51.2–32.6% with strategy II). In 2019, if HighR-CHRs had delivered only LS negative flocks, the RR would have reduced from 0.94 (scenario “O”) to 0.51 (A-I). Other scenarios showed smaller RR reductions. Targeting high risk farms/flocks for intensive control could improve One Health-ness of national action plans against Campylobacter spp.