Rickettsia typhi is the etiologic agent of both epidemic and endemic typhus. Serologic testing is used to confirm the diagnosis and requires acute- and convalescent-phase serum samples.
Tabs Content Clinical Overview Diagnosis
Indications for Testing
Fever, headache, chills, rash, dry cough, nausea, and vomiting in at-risk individual (living in unsanitary conditions, close human contact, with potential for mouse/rat contact)
Laboratory Testing
Clinical presentation and diagnosis recommendations (CDC)Nonspecific
CBC
Hepatic transaminases
Bilirubin
Blood urea nitrogen (BUN)
Creatinine
IgG and IgM by indirect fluorescent antibody (IFA) – use to confirm diagnosis
Convalescent specimen usually required
IgG does not differentiate between primary infection and Brill-Zinsser disease
Febrile antibody testing
More specific than Weil-Felix but still has cross-reactivity with Brucella Salmonella
Must be used in conjunction with clinical presentation
Weil-Felix
Not sensitive or specific
Outmoded
Should not be used
Culture – not routinely available because of biosafety issues (research labs only)
Differential Diagnosis
Background
Epidemiology
Incidence – <100 cases annually in the U.S.
Transmission – louse or flea
Organism
Gram-negative coccobacilli of the Rickettsiaceae family (obligate intracellular organisms)
Characteristic feature of Rickettsia – life cycle requires multiplying in an arthropod
With typhus (R. prowazekii and R. typhi ), the invertebrate hosts are both reservoirs and vectors
Rickettsia are part of a family of organisms responsible for the following rickettsial diseases
Risk Factors
Epidemic typhus (louse borne) – residence in poor hygienic areas (eg, jails) in cold months
Endemic murine typhus (flea borne) – residence in close-quartered poverty in warm climates
Recrudescent typhus (Brill-Zinsser disease) – previously acquired disease combined with immunosuppression or old age
Flying squirrel typhus (louse or flea borne) – contact with flying squirrels, particularly in southern U.S.
Clinical Presentation
Incubation period – 3-14 days
Most patients develop nonspecific symptoms and signs
Onset of disease is sudden in about half of the cases
Fever and headache are the most commonly reported symptoms
Chills, myalgias, arthralgias, malaise, and anorexia can be present
Rash (maculopapular, nonconfluent, and blanching areas)
Hallmark of infection
Usually follows systemic symptoms
Often transient and difficult to observe in murine typhus
Absence should not rule out a possible rickettsial etiology
Pulmonary involvement is frequent in murine typhus
Serious central nervous system impairment can also be seen with typhus
Meningitis Seizures
Hearing loss
Multiorgan failure may occur
ARUP Lab Tests
Confirm presence of Rickettsia typhi
Not recommended for initial testing; requires comparison of acute- to convalescent-phase serology
While presence of IgM antibodies suggests current or recent infection, low levels of IgM antibodies may occasionally persist for >12 months postinfection
Any antibody reactivity to R. typhi antigen should also be considered group reactive for typhus fever group (R. prowazekii)
If test results are equivocal, repeat testing in 10-14 days
Confirm presence of disease
Not recommended for initial testing
Nonspecific testing for R. typhi
Initial screening for hepatobiliary inflammation
Nonspecific testing for R. typhi
Screening test to evaluate kidney function
Nonspecific testing for R. typhi
Screening test to evaluate kidney function
Nonspecific testing for R. typhi
Assay interference (negative) may be observed when high concentrations of N-acetylcysteine (NAC) are present
Negative interference has also been reported with NAPQI (an acetaminophen metabolite), but only when concentrations are at or above those expected during acetaminophen overdose
Confirm presence of R. typhi
Panel test (IgG and IgM) is preferred
Requires comparison of acute- to convalescent-phase serology
References Chapman AS, Bakken JS, Folk SM, Paddock CD, Bloch KC, Krusell A, Sexton DJ, Buckingham SC, Marshall GS, Storch GA, Dasch GA, McQuiston JH, Swerdlow DL, Dumler SJ, Nicholson WL, Walker DH, Eremeeva ME, Ohl CA, Tickborne Rickettsial Diseases Working Group, CDC. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other health-care and public health professionals. MMWR Recomm Rep. 2006; 55(RR-4): 1-27. PubMed Huntzinger A. Guidelines for the diagnosis and treatment of tick-borne rickettsial disease . Am Fam Physician. 2007; 76(1): 137-139. Leawood, KS [Accessed: Nov 2017] Bechah Y, Capo C, Mege J, Raoult D. Epidemic typhus. Lancet Infect Dis. 2008; 8(7): 417-26. PubMed
Brouqui P, Raoult D. Arthropod-borne diseases in homeless. Ann N Y Acad Sci. 2006; 1078: 223-35. PubMed
Civen R, Ngo V. Murine typhus: an unrecognized suburban vectorborne disease. Clin Infect Dis. 2008; 46(6): 913-8. PubMed
Delord M, Socolovschi C, Parola P. Rickettsioses and Q fever in travelers (2004-2013). Travel Med Infect Dis. 2014; 12(5): 443-58. PubMed
Walker DH, Paddock CD, Dumler S. Emerging and re-emerging tick-transmitted rickettsial and ehrlichial infections. Med Clin North Am. 2008; 92(6): 1345-61, x. PubMed
Related Topics Last Update: October 2019
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