We performed this cross-sectional study in order to identify litter- and herd-level factors affecting the odds of occurrence and the level of I. suis oocyst excretion in nursing piglets of Greek farrow-to-finish herds. Alterations in managerial practices and environmental factors are likely to contribute to the control of isosporosis through the reduction rather than the elimination of oocyst excretion, at least in the medium term. Thus, from an epidemiological point of view, there is an interest in the identification of risk factors that reduce the risk and/or the level of oocyst excretion. The majority of the candidate risk/preventive factors, and those in the final model, can be considered constant over time since they represent either routine managerial practices or refer to properties of housing facilities. They were not subject to modification depending on the perceived or observed oocyst excretion risk and, hence, minimized the limitations arising from the cross-sectional design. This design, however, may not have captured the well-accepted daily variation in oocyst excretion levels. This may explain the fact that the majority of the factors identified in our analysis were associated with the odds and not the level of oocyst excretion (Table 2).
Application of early routine treatment with toltrazuril reduced both the odds and the level of oocyst excretion. The efficacy of this treatment against piglet coccidiosis has been previously demonstrated in experimentally infected piglets [36, 37] as well as under natural infection conditions [19, 21, 38, 39]. Toltrazuril affects all endogenous parasite stages  and suppresses the development of oocysts . Treatment delays the onset of oocyst excretion and decreases both the odds of oocyst excretion and the mean amount of excreted oocysts . Therefore, it lowers infection pressure and contributes to a slower and incomplete spread of I. suis, until piglets are sufficiently resistant to both infection and clinical isosporosis [17, 37].
Herds practising cross-fostering of piglets after day one p.f., had litters with higher odds of oocyst excretion compared to litters in herds where cross-fostering was not applied or done within the first 24 hours p.f. Late cross-fostered piglets may shed earlier and may be responsible for litter over-contamination. Early fostering reduces exposure of piglets to the stress of fostering. The severity and duration of diarrhoea are greater and earlier in cross-fostered piglets compared with resident counterparts despite that fact that the former excrete less oocysts [17, 19]. The latter may be partly ascribed to the absence of a solid immunity status in late cross-fostered piglets , which are moved in an environment with pathogens against which they do not have adequate protection. Further, late cross-fostering could lead to the introduction of piglets from an infected litter to an uninfected one or one with low shedding.
Cleaning and disinfecting the entire farrowing room after all litters were weaned reduced the odds of oocyst excretion. The proposed approach is an indication of a relatively high standard in the practiced hygiene procedures in a farm, as part of an integrated all-in-all-out management. Reduced environmental contamination, by thorough cleaning, can be effective in preventing or delaying initial I. suis infections in very young suckling piglets  and farms applying above-average hygiene measures have decreased infection rates . Cleaning the entire farrowing room at once, instead of cleaning the pen of each weaned litter, provides a simultaneous and homogeneous reduction of the contamination level in all pens. Complete removal of oocysts from the environment is practically unfeasible; however, lower infection pressure can reduce the odds of clinical disease , initiating a slower and incomplete spread of the disease .
We failed to identify a significant association of the perforated proportion of pen flooring with the odds or the level of oocyst excretion. However, a significant effect was observed for the type of perforated flooring: plastic flooring decreased the risk of oocyst excretion compared to metal flooring. Likely, this is because plastic flooring is a material that can be easily and effectively cleaned, thus, leading to a reduced number of ingested oocysts. Metal flooring, compared with plastic, is harder to maintain clean , thus the applied sanitary procedures could more effectively remove infectious oocysts in farrowing pens with plastic flooring, compared to metal flooring, resulting in decreased infection pressure for the successive litter.
Litters in farrowing rooms with large number of farrowing pens had decreased odds of occurrence of oocyst excretion. An important route of I. suis transmission, besides the one between successive litters (one generation of piglets to the next), is from one oocyst excreting litter to a neighbouring one, via mechanical carriers . The aforementioned between-pen transmission and eventually built-up of the environmental contamination may be favoured in smaller than larger farrowing rooms. Smaller rooms may be looked after by only one caretaker while this may be less likely in larger units. Room size was correlated (P = 0.03) with the number of caretakers employed in that section. Furthermore, the size of the farrowing room may be considered as a proxy variable for a mixture of good managerial practices which are more consistently and efficiently adhered to in larger farms.
The presence of more than two caretakers in the farrowing section resulted in decreased odds of oocyst excretion. The existence of more caretakers could provide adequate manpower to maintain a relatively constant and high level of hygiene. Moreover, hygiene is sometimes neglected during work-intensive periods , thus more caretakers, regardless of herd size, can ensure a higher ratio of labour dedicated to cleaning. In some herds all routine manipulations in piglets by caretakers were carried out without them entering in the farrowing pens. Those litters had a lower infection level, as expressed by lower oocyst excretion. This practice has been proposed as an additional preventive measure for control of isosporosis. Limited access of farm workers to pens, with possibly infected piglets, can prevent pen-to-pen spread of infection via mechanical transfer of oocysts with boots . Furthermore, others  suggested that the most important route of transmission is not from one litter to the next within the same pen, but more likely from one oocyst excreting litter of piglets to a neighbouring litter of younger and highly susceptible piglets, for example, via contaminated boots of the animal caretaker.