The Isolation of Orientia tsutsugamushi and Rickettsia typhi from Human Blood through Mammalian Cell Culture: a Descriptive Series of 3,227 Samples and Outcomes in the Lao People's Democratic Republic.

Damien K Ming,Stuart D Blacksell,Phonepasith Panyanivong,Paul N Newton,Vilada Chansamouth,Vanheuang Phommadeechack,Matthew T Robinson,Tamalee Roberts,Weerawat Phuklia,Davanh Sengdatka,Bobbi S Pritt

doi:10.1128/jcm.01553-20

Abstract

In the Lao People's Democratic Republic (Laos), rickettsial infections, including scrub and murine typhus, account for a significant burden of fevers. The Mahosot Hospital Microbiology Laboratory in Vientiane, Laos, routinely performs rickettsial isolation from hospitalized patients with suspected rickettsioses using mammalian cell culture systems. We review the clinical and laboratory factors associated with successful Orientia tsutsugamushi and Rickettsia typhi isolations from this laboratory over a period of 6 years between 2008 and 2014. The overall isolation success was 7.9% for all samples submitted and 17.3% for samples for which the patient had a positive O. tsutsugamushi or R. typhi rapid diagnostic test (RDT), serology, or PCR. The frequency of successful isolation was highest for samples submitted in November, at the end of the wet season (28.3%). A longer median duration of reported illness, a positive result for a concurrent Orientia or Rickettsia spp. quantitative PCR, and the use of antibiotics by the patient in the week before admission were significantly associated with isolation success (P < 0.05). Buffy coat inoculation and a shorter interval between sample collection and inoculation in the laboratory were associated with a higher frequency of isolation (both P < 0.05). This frequency was highest if cell culture inoculation occurred on the same day as blood sample collection. Factors related to the initial rickettsial bacterial concentration are likely the main contributors to isolation success. However, modifiable factors do contribute to the rickettsial isolation success, especially delays in inoculating patient samples into culture.

Highlights

In the Lao People’s Democratic Republic (Laos), rickettsial infections, including scrub and murine typhus, account for a significant burden of fevers
There are studies which describe culture conditions used in rickettsial isolation [16], there are none to our knowledge which examine the clinical or laboratory factors associated with successful isolation of O. tsutsugamushi and R. typhi
A total of 3,227 EDTA-anticoagulated whole blood samples were received for rickettsial isolation from 3,200 patients recruited into fever studies conducted in Vientiane (n ϭ 1,064; 33.0%), Luang Namtha (n ϭ 1,543; 47.8%), and Salavan (n ϭ 620; 19.2%) between January 2008 and December 2014

Summary

Introduction

In the Lao People’s Democratic Republic (Laos), rickettsial infections, including scrub and murine typhus, account for a significant burden of fevers. The Mahosot Hospital Microbiology Laboratory in Vientiane, Laos, routinely performs rickettsial isolation from hospitalized patients with suspected rickettsioses using mammalian cell culture systems. We review the clinical and laboratory factors associated with successful Orientia tsutsugamushi and Rickettsia typhi isolations from this laboratory over a period of 6 years between 2008 and 2014. Scrub typhus, caused by O. tsutsugamushi, is the main contributor to this burden and an underrecognized disease affecting predominantly rural areas with poor health infrastructure [1] This disease is transmitted through inoculation by infected chigger mites and is responsible for between 1.8% and 22.3% of fevers among inpatients, depending on region [2, 3], with a median, untreated mortality of approximately 6% [4]. We undertook a retrospective review of laboratory data at Mahosot Hospital for samples collected for rickettsial culture over 6 years between January 2008 and December 2014

Methods

Results

Conclusion