Selection of Diagnostic Cutoffs for Murine Typhus IgM and IgG Immunofluorescence Assay: A Systematic Review

Abstract

. Murine typhus is a neglected but widespread infectious disease that results in acute fever. The immunofluorescence assay (IFA) is the “gold standard” to identify IgM or IgG antibodies, although there is a lack of standardization in methodologies. The objective of this review is to summarize 1) the differences in published methodologies, 2) the diagnostic cutoff titers, and 3) the justification of diagnostic cutoffs. Searches were performed by combining the following search terms: “murine typhus,” “ rickettsia typhi ,” “immunofluorescence,” “IFA,” and “serologic” with restrictions (i.e., “ rickettsia typhi ” or “murine typhus,” and “IFA” or “immunofluorescence,” or “serologic*”). The search identified 78 studies that used IFA or immunoperoxidase assay (IIP) antibody cutoffs to diagnose murine typhus, 39 of which were case series. Overall, 45 studies (57.7%) provided little to no rationale as to how the cutoff was derived. Variation was seen locally in the cutoff titers used, but a 4-fold or greater increase was often applied. The cutoffs varied depending on the antibody target. No consensus was observed in establishing a cutoff, or for a single-value diagnostic cutoff. In conclusion, there is a lack of consensus in the establishment of a single-value cutoff. Further studies will need to be executed at each distinct geographic location to identify region-specific cutoffs, while also considering background antibody levels to distinguish between healthy and infected patients.

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

“…However, known limitations in IFA performance, the requirements for convalescent sera, and a lack of standardisation can make interpretation of serology difficult (11). Other tests such as enzyme linked immunosorbent assays (ELISAs) on October 31, 2020 by guest http://jcm.asm.org/ Downloaded from and nucleic acid amplification from clinical specimens can be helpful (12). The in vitro isolation of Orientia and Rickettsia spp.…”

An Update on the Laboratory Diagnosis of Rickettsia spp. Infection

“…Further issues with serological diagnosis include the lack of standardisation for IFA cut-off values or the antibody isotypes used (IgM, IgG, or whole Ab) [ 38 , 39 , 40 , 41 ]. For example, in the diagnosis of murine typhus, the IgG positivity cut-off titre ranges from ≥ 1:40 in Spain to > 1:960 in Nepal [ 38 ].…”

“…Further issues with serological diagnosis include the lack of standardisation for IFA cut-off values or the antibody isotypes used (IgM, IgG, or whole Ab) [ 38 , 39 , 40 , 41 ]. For example, in the diagnosis of murine typhus, the IgG positivity cut-off titre ranges from ≥ 1:40 in Spain to > 1:960 in Nepal [ 38 ]. Determining accuracy for positive and negative results is dependent on an understanding of background immunity in endemic and non-endemic settings [ 21 ].…”

“…Anti-rickettsial antibodies can remain detectable for months (IgM) to years (IgG) after an infection, which makes it challenging to differentiate acute infection from a sub-clinical infection or previous exposure [ 22 ]. In endemic settings, higher diagnostic cut-off values have been suggested, with locally validated positivity cut-off values where possible [ 38 , 41 ]. Region-specific ELISA OD diagnostic cut-offs based on local epidemiology are also required.…”

Manifestations and Management of Flea-Borne Rickettsioses

“…Although a higher cutoff titer in some areas may be in order, 147 the regional seroprevalence to optimize these cutoffs is often unknown. 148 …”