Table 3.

Parameters derived from sequential serological testing of 54 camels on 10 rounds at 10-day intervals

Parameter1	Level, number of values (unit)	Definition / calculation
Duration of seropositivity	Individual camel level, single value across all sampling rounds (days).	Number of consecutive rounds when camel tested positive*10 days.
Antibody level increase (serological indication of infection)	Individual camel level, 9 values, one for each sampling round except the first (binary event).	When, in the current sampling round, either status of camel changes from seronegative to seropositive or the OD ratio more than doubles compared to that of the previous sampling round.
Number of positive tests	Individual camel, single value across all sampling rounds (discrete number of events from 0 to 10).	Total number of sampling rounds when the camel was found to be seropositive.
Incidence rate2	Whole herd, single value across all sampling rounds (cases per camel days at risk).	Number of new “cases” observed during the entire follow-up period over the cumulative sum of camel’s time at risk, with a “case” being an antibody level increase as defined above.
Antibody level stability	Camel, single value across all sampling rounds. Only assessed for camels that tested positive at least once (binary event).	A camel is considered to exhibit antibody level stability if its OD ratio did not increase by more than 100% or decrease by more than 50% during the study period.
Seroprevalence	Sampling round for whole herd (proportion).	Number of camels found to be seropositive at a given sampling round over the total number of camels tested at the same round.

¹ Borderline considered negative.

² Cumulative sum of camel time at risk obtained assuming that a camel is always at risk of experiencing antibody titer increase.