If eggs were merely a generic Salmonella vehicle, the egg-association rate would be similar across serotypes. Instead SE outbreaks were egg-associated about three times more often (44% vs 15%) than outbreaks of other Salmonella serotypes. This differential ties the egg vehicle specifically to SE, and the epidemic rise specifically to SE, consistent with a biological route (trans-ovarian colonization of the hen’s reproductive tract) available to SE but not equally to other serotypes, which contaminate mainly via feces/environment/surface. The serotype specificity strengthens the causal claim that SE-contaminated eggs — not eggs as a generic Salmonella source — drive the epidemic (H-12). It is still surveillance data, so vehicle-identification bias (eggs being more readily suspected/traced) cannot be fully excluded.
Validity verdict — approved (checked)
Reconstruction. Premises (taken as given for validity): SE outbreaks were egg-associated 44% of the time vs 15% for other Salmonella serotypes. Hidden load-bearing premise, in its strongest charitable form: a generic (non-serotype-specific) egg vehicle would produce roughly equal egg-association rates across serotypes, so a large serotype differential is more expected under an SE-specific egg route than under a generic Salmonella-egg association. Conclusion: the differential is evidence that the egg link is specific to SE (supporting H-12’s SE-specific vehicle over a generic one).
Evaluation of the step. Conditional on the numbers, the inference is a valid likelihood/evidential move: a ~3× differential is genuinely better predicted by “egg vehicle available specifically to SE (e.g. trans-ovarian colonization) than to other serotypes” than by “eggs are a generic Salmonella source.” The candidate undercutting defeater is ascertainment / vehicle-identification bias — during 1973–1984 SE was rising and eggs were the prime suspect, so SE outbreaks may be preferentially traced to eggs, inflating the 44% without an SE-specific biological route. This defeater operates conditional on the raw rates and does reduce the strength of the inference, but it does not reverse or eliminate the evidential direction: the differential still raises the probability of the SE-specific-vehicle hypothesis relative to the generic one. Because the statement is already framed evidentially (“indicates … supporting …” rather than “proves”), the surviving weaker-strength inference is exactly the claim as stated. No defeater breaks the reason→conclusion link at the evidential level, so it holds as stated. Author-blind; the step is a simple contrastive-likelihood argument I traced directly. Approved / checked.