We analyzed factors involved in the introduction of infectious laryngotracheitis (ILT) virus (ILTV) onto broiler farms during a localized outbreak in an immunologically naïve broiler population. The outbreak occurred in the state of Mississippi, United States in 2002–2003. From the responses to a retrospective survey questionnaire administered via personal interviews, 181 farm-level risk factors were defined and analyzed for their association with ILTV introduction using logistic regression. There were 27 case farms (93% of all the infected broiler farms) and two sets of controls: farms matched to the cases by location and those randomly selected among the broiler farms in Mississippi. We found that farm suppliers such as gas company representatives, who are likely to visit other farms, and farm-workers who visit other chicken farms, are likely vehicles of ILTV introduction onto broiler farms. These risks can be greatly reduced by following biosecurity procedures, in particular if farm workers bathe and change footwear prior to entering broiler houses on their own farm. Footbaths for farm visitors can provide a false sense of security during an ILT outbreak when, indeed, other practices such as plastic boots or changing boots are more effective in preventing ILTV transmission. Sharing of equipment used for removal of caked broiler litter between subsequent flocks may also serve as an important vehicle of ILTV transmission. During the 2002–2003 outbreak, shared litter removal equipment was associated with ILTV transmission despite a requirement being put in place for litter decontamination. We also found that tunnel-ventilated broiler houses with inlets toward a neighboring poultry farm are more likely to get infected with ILTV. In addition to this analysis, the data collected provide a good overview of the actual practices and deficiencies of biosecurity undertaken on broiler farms in this part of the United States.
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Vol. 56 • No. 3