Sero-prevalence of spotted fever typhus and scrub typhus group rickettsioses among patients with acute febrile illiness in Kenya.

Abstract

Rickettsiosis is a pathogenic bacterial infection which is rarely identified as a cause of illness in patients presenting with common symptoms such as fever and headache. In any case, rickettsiae are difficult to diagnose especially in health facilities with limited diagnostic capability. Reported cases of rickettsioses among travelers to the Kenyan games parks have contributed to increased awareness of this disease. Unfortunately, very little is known about this disease among Kenyans. To address this knowledge gap, this study aimed at determining the sero-prevalence of the spotted fever group (SFG), typhus group (TG) and scrub typhus (ST) rickettsioses in patients presenting with acute febrile illness (AFI) at clinical sites across different regions in Kenya. The study enrolled 2225 participants >1 year who presented with fever (> 38 C) without a readily diagnosable cause of infection. The study began in March 2008 to 2012 and collected blood samples for serum preparation from patients attending health facilities in different parts of Kenya: Kisii highlands (Kisii District Hospital), Kisumu (Obama Children’s Hospital and Kisumu District Hospital), Busia (Alupe District Hospital), Marigat (Marigat District Hospital), Garissa (Iftin Subdistrict hospital, Garissa Police Line dispensary and at the Kenyan coast (Malindi District Hospital). A total of 2225 archived sera were all were tested for antibodies to SFG (100%), 1611 (72.4%) to TG and 1401 (63.0%) to ST rickettsioses by ELISA.212/2225 (9.5%) were sero-positive for SFG (95% C.I 8.3-10.7), 4/1611 (0.2%) for TG (95% CI, 0.0 –0.5) and 67/1401 (4.8%) for ST (95% CI, 3.7–5.9).A higher prevalence rate was seen in Garissa (57/226, 25.2%) than in Alupe (27/176, 15.3%), Marigat (37/320, 11.6%), Malindi (9/102, 8.8%), Kisii (39/656, 5.9%), or Kisumu (43/745, 5.8%).Of the total sera, (36.8%) had a titer of 1:1600 and 1:6400 (38.2%) with the highest number reported from Garissa. Antibodies to TG were only seen in Malindi (3/4, 75%) and Kisumu (1/4, 25%). Sero-prevalence of ST was highest in Marigat 28/238 (11.8%) followed by Alupe 4/68 (5.9%), Garissa 6/134 (4.5%), Kisumu 19/464 (3.5%), and Kisii 10/458 (2.2%). No cases of ST were noted in Malindi. 62.7% of individuals had a titer of 1:400, with 45.2% coming from Marigat. Significant associations were found between males and females with higher sero-prevalence among females (43/694, 6.2%) compared to males (24/707, 3.4%) (P=0.017) and between the different age groups for both SFG and ST (P <0.0001), and between sero-positivity and having animal contact with dogs (P=0.0296) and camels (P <0.0001) for SFG and goats for ST (P=0.0003) and between having symptoms (headache, joint ache and muscle ache) and ST and SFG (P<0.0001) seropositivity. In conclusion, SFG and ST rickettsioses are common among patients with acute febrile illness in Kenya. This is the first report of scrub typhus in Kenya. The findings of this study suggest that rickettsial infections should be considered in the differential diagnosis of febrile cases in Kenya and that diagnostic capacity with health facilities should be established.