TNR/RTF and the AAFP feline retrovirus management guidelines

The American Association of Feline Practitioners guidelines to managing retroviral diseases in cats say the following about testing cats in TNR (and by extension, Return to Field) programs:
Although this document broadly recommends testing all cats for retroviral infection, an exception
exists for feral cats in trap-neuter-return (TNR) programs. The prevalence of infection is similar in outdoor pet cats and feral cats; so feral cats do not present an increased threat to pets (Levy et al 2006b).

Additionally, neutering reduces two common modes of transmission: queen to kitten for FeLV and fighting among males for both FeLV and FIV (Levy 2000, Levyv and Crawford 2005).

Because population control of feral cats requires commitment to neutering the largest number of cats possible, many TNR programs do not routinely test feral cats (Wallace and Levy 2006).