Rocky Mountain Spotted Fever - Reliability of Tests and Clinical Presentations

According to an article published in the American Journal of Tropical Medicine and Hygiene, the current testing for IgM and IgG antibodies in Rocky Mountain spotted fever patients is highly unreliable (McQuistman, Weidman et al. 2014). The researchers particularly draw attention to disparities between IgM and IgG responses in confirmed cases of RMSF. As it goes, IgM was seen in 6 of 13 patients (46%) without a corresponding development of IgG antibodies. This means that nearly half of the patients in this study never developed IgG antibodies.


Inadequacy of IgM Antibody Tests for Diagnosis of Rocky Mountain Spotted Fever
Article link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4183402/

Abstract:
Among 13 suspected Rocky Mountain spotted fever (RMSF) cases identified through an enhanced surveillance program in Tennessee, antibodies to Rickettsia rickettsii were detected in 10 (77%) patients using a standard indirect immunofluorescent antibody (IFA) assay. Immunoglobulin M (IgM) antibodies were observed for 6 of 13 patients (46%) without a corresponding development of IgG, and for 3 of 10 patients (30%) at least 1 year post-onset. However, recent infection with a spotted fever group rickettsiae could not be confirmed for any patient, based on a lack of rising antibody titers in properly timed acute and convalescent serologic specimens, and negative findings by polymerase chain reaction testing. Case definitions used in national surveillance programs lack specificity and may capture cases that do not represent current rickettsial infections. Use of IgM antibodies should be reconsidered as a basis for diagnosis and public health reporting of RMSF and other spotted fever group rickettsiae in the United States.

My issue:

I recently tested for RMSF through Labcorp and did have a low response on my IgG, albeit not a "positive" IgM according to Labcorp. My doctor said that the results were in essence negative as the detected levels were low and there was no IgG present. Given that I am six years away from my initial infection, I surmise that the IgM would be weak and perhaps even the IgG would be absent.

Questions for the community:

1) As with borrelia, shouldn't the presence of any antibodies indicate a positive infection?

2) Have any of you personally been diagnosed with RMSF? If so, please explain.

3) What testing is available to test rickettsial infections in the broader spectrum?

Really? I got the opposite opinion from Buhner's 2nd edition, where he goes into greater length of the "Spotted Fever" as he calls it, than I've ever seen before.

My basic, run of the mill lab test found it, and I'm sure I'd had the infection for many years prior. And even the second test I did 2 weeks later found it again.

Somebody said...
I had a positive igg negative igm through labcorp. The positive was low positive. I was told it could be false positive. Also due to the low positive value they seemed to think whatever abx I took handled it.

k07, how long after your symptoms started to develop did you have the test done?

k07 said...
I had a positive igg negative igm through labcorp. The positive was low positive. I was told it could be false positive. Also due to the low positive value they seemed to think whatever abx I took handled it.

I never had the classic rmsf rash. Did have summer flu.

I don't know if I did either. I have a couple different kinds of rashes in my infection history but the first one was labeled shingles simply on observation, and the second one never did get identified. The Dr. had no idea. I thought it was some kind of poisonous plant contact because I'd been pulling weeds just before, but he insisted it didn't look like it. So, maybe that was when I got the RMSF. I'm not sure everyone does, much like not everyone gets the bullseye rash.

k07 said...
What state are you guys in?

Pennsylvania

I had all the symptoms of RMSF when I was 7 yrs old. I had no rash though, which is an atypical presentation, and it was back in 1970, and in California - so it was 'unheard of' and I was not diagnosed properly, nor did I get good treatment.

In 2008, after a full year of treatment for Lyme, I finally tested fully CDC positive for Lyme and RMSF.