Table 1. Infection data recorded for 677 case-patients in historical studies of Plasmodium vivax infection, circa 1920–1980*.

Infection data	No. (%) patients
Neurosyphilis/neurologic treatment patient	433 (64.0)
Recorded data
Exact incubation period only	356 (52.6)
Time to relapse only	217 (32.1)
Exact incubation and time to relapse	104 (15.4)
Infected with
Tropical strains	275 (40.6)
Temperate strains	402 (59.4)
New World strains	181 (26.7)
Old World strains	496 (73.3)

*The study population was followed for a mean of 82.5 weeks (SD 31.7, range 2.0–173.0).