Distinguishing Japanese Spotted Fever and Scrub Typhus, Central Japan, 2004- 2015

Abstract

Japanese spotted fever (JSF) and scrub typhus (ST) are endemic to Japan and share similar clinical features. To document the clinical and epidemiologic characteristics that distinguish these 2 rickettsial diseases, during 2004-2015 we recruited 31 JSF patients, 188 ST patients, and 97 nonrickettsial disease patients from the southern Boso Peninsula of Japan. JSF occurred during April-October and ST during November-December. Patients with JSF and ST were significantly older and more likely to reside in wooded areas than were patients with nonrickettsial diseases. Spatial analyses revealed that JSF and ST clusters rarely overlapped. Clinical findings more frequently observed in JSF than in ST patients were purpura, palmar/plantar rash, hyponatremia, organ damage, and delayed defervescence after treatment. Although their clinical features are similar, JSF and ST differ in seasonality, geographic distribution, physical signs, and severity. Because a considerable percentage of patients did not notice rash and eschar, many rickettsial diseases might be underdiagnosed in Japan.

Keywords: Japan; Japanese spotted fever; Orientia tsutsugamushi; Rickettsia; Rickettsia japonica; scrub typhus; tsutsugamushi disease.

Figure 1

Numbers of patients with rickettsial or nonrickettsial diseases, Japan, 2004–2015. Of 43 patients tested by immunofluorescence and immunoperoxidase assays, 4 fulfilled the criteria for having confirmed JSF, 7 for confirmed ST, and 7 for probable ST. Gray shading indicates the cases included in the main analysis. JSF, Japanese spotted fever; MT, murine typhus; non-R, nonrickettsial disease; ST, scrub typhus.

Figure 2

Number of patients with Japanese spotted fever, scrub typhus and nonrickettsial diseases, central Japan, by month, 2004–2015.

Figure 3

Geographic distribution and clusters of JSF and ST, Japan, 2004–2015. A) JSF; B) ST; C) geographic clusters of JSF and ST; D) locations of study facilities. White diamonds (JSF) and circles (ST) represent the locations of each patient’s address. Colored circles (black, JSF; gray, ST) represent statistically significant spatial clusters (p<0.05). The geographic distribution of the patients with nonrickettsial diseases, which were used for the cluster analysis as the reference, is shown in the Technical Appendix Figure). ARMEC, Awa Regional Medical Center; JSF, Japanese spotted fever; KFCT, Kameda Family Clinic Tateyama; KMC, Kameda Medical Center; ST, scrub typhus.