Seroprevalence of Q-fever, spotted fever, typhus group Rickettsia and Orientia among febrile patients visiting hospital-based sentinel sites in Uganda: A cross-sectional study

Abstract

Introduction: rickettsioses are emerging zoonotic
febrile illnesses transmitted to humans by ticks,
fleas, lice, and mites. Q-fever, Spotted fever group
(SFG), Typhus group (TG) rickettsia and Scrub
typhus (STG) have been reported with varying
prevalence across East Africa. However, little is
known about the burden of exposure in Uganda.
The aim of this study was to determine the
seroprevalence and associated risk factors of
rickettsial diseases in Uganda. Methods: a total of
460 archived serum samples collected from
patients with fever of unknown origin after
screening across five hospital-based sentinel sites
were analysed. The samples were collected during
18-month period of active surveillance for acute
febrile illnesses, from January 2018 through June
2019. We performed IgM ELISA tests on the 460
sera for SFG and TG rickettsia, IgM IFA for STG and
Phase 2 IgG ELISA for Q-fever. We also assessed
risk factors associated with the serostatus. Results:
the population comprised predominantly children,
had balanced gender proportions, with 66%
coming from rural areas. The overall
seroprevalence of SFG rickettsiosis was 6.3%; however, 11.5% and 10.8% prevalence rates were
observed in Gulu and Bwera hospitals respectively.
This was higher than the 3.7% observed in the
capital city Kampala, although the differences
were not statistically significant (Fisher's exact =
0.489). Overall seropositivity of Q-fever was 7.6%,
although Bwera Hospital had the highest rate
(12.5%) and Mulago had the lowest rate (2%). The
differences were not considered statistically
significant (Fishers exact= 0.075). Increasing age
(OR-adjusted=1.4, 95%CI=1.0-1.9, p=0.026) and
rural background (OR-adjusted=2.6, 95%CI=1.6-
6.4, p=0.037) were both significantly associated
with seropositivity for Q-fever, while only
increasing age had higher odds for seropositivity
for SFG rickettsia (OR-adjusted= 1.9, 95% CI= 1.4-
2.6, p<0.001). One serum sample of a 10-monthold male from Bwera hospital was reactive to both
SFG and Q-fever antibodies. We found four sera
reactive cases to typhus group IgM and another
four reactive to Orientia spp. IgM. However, we
were not able to determine associating factors due
to low seropositivity rates. Conclusion: here, we
report for the first time the seroprevalence of Qfever, SFG and STG in febrile patients in Uganda.
This report also provides the second study in over
five decades since the earliest report of TG
rickettsia. Testing for these pathogens in patients
with acute febrile illness with unknown etiology
may hold value, however more studies are
required to provide information on disease
ecology, risk factors, and transmission dynamics of
these pathogens in Uganda.