During 1994, 37 cases of Plasmodium malariae parasitemia were reported from the malaria center in Ahssa region of the Kingdom of Saudi Arabia (KSA). Local transmission was suspected since these cases represented 68% of all P. malariae diagnosed in Saudi Arabia. Before 1950, Ahssa had endemic malaria, but since 1970 transmission has been interrupted. However, the vector Anopheles stephensi is still present.
Methodology
In May 1995 we reviewed all reports of P. malariae registered in the Ahssa malaria center. We defined a case of P. malariae as any case from Ahssa diagnosed from January 1994 through May 1995. A case control study was conducted and a questionnaire designed including information regarding domestic habits and conditions. For each case, five controls were selected from the residence permit list of the malaria center. The controls matched cases nationality, sex and age.
Results
From January 1994 through May 1995, 37 persons with symptomatic P. malariae parasitemia, all from malaria endemic countries, were detected in Ahssa. The 37 cases had no seasonal or geographic pattern; but 22 (61%) had onset of fever within 70 days of arrival to Saudi Arabia (probably imported), of which 19 (86%) had arrived from India. We located and interviewed 14 of these Indian cases and their corresponding controls. In this group, P. malariae infection was associated with documented (by passport) transit for several nights (median 7) through Bombay before departing India for Saudi Arabia (OR=16, P ≤ 0.05). We were able to interview 7 of the 15 cases with onset after 70 days of arrival and their controls. Among this group there was an association with sleeping in an open field (OR=16, CI 1.2-222), and a preference for injection for medical treatment (OR=undefined, CI=3.7-infinity).
Conclusion
The association of imported P. malariae in recently arrived Indian workers who had stayed in Bombay is supported by recent reports of malaria outbreaks in Bombay. The association of indication of local malaria exposure (injection and sleeping outdoors) could represent local transmission but is subject to recall bias. The continuing importation and possible local transmission will require improved surveillance with prompt epidemiologic and entomologic case investigation to identify and control introduced malaria transmission.