|Year : 2017 | Volume
| Issue : 2 | Page : 121-124
Validation of a clinical score to differentiate scrub typhus and dengue
Surendra Kumar Mutyala1, Shubhanker Mitra2, Kundavaram Paul Prabhakar Abhilash1, Vishalakshi Jayaseelan3
1 Department of Emergency Medicine, Christian Medical College, Vellore, Tamil Nadu, India
2 Department of General Medicine, Christian Medical College, Vellore, Tamil Nadu, India
3 Department of Biostatistics, Christian Medical College, Vellore, Tamil Nadu, India
|Date of Web Publication||18-May-2017|
Kundavaram Paul Prabhakar Abhilash
Department of Emergency Medicine, Christian Medical College, Vellore - 632 004, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Background: Scrub typhus and dengue are two major causes of acute undifferentiated febrile illness in many parts of India and are difficult to differentiate at initial presentation. Materials and Methods: This retrospective observational study was conducted in a large emergency department (ED) between September 2014 and December 2014. The clinical score to differentiate scrub typhus and dengue (CSSD) was validated on confirmed cases of scrub typhus and dengue who presented during the study period. The six variables used in CSSD were SpO2, hemoglobin, total white blood cell count, serum glutamic oxaloacetic transaminase level, serum bilirubin, and sensorium. Results: During the study period, 134 confirmed cases of scrub typhus and dengue were included in the analysis, of which 68 were scrub typhus and 66 were dengue. A male predominance was seen in dengue (60.6%), whereas females comprised the majority in scrub typhus (58.8%). Among 68 confirmed cases of scrub typhus, 32 patients have CSSD score <13, favoring scrub typhus. Among 66 confirmed cases of dengue, 64 patients have CSSD score ≥13, favoring dengue. CSSD has high specificity (97%) and positive predictive value (94%) for scrub typhus patients. CSSD score has high sensitivity (97%) and negative predictive value (94%) for dengue patients. Conclusion: The CSSD is a simple and inexpensive score that can be done rapidly at initial presentation of the patient to the ED. It has a high specificity and positive predictive value for scrub typhus and high sensitivity and negative predictive value for dengue and can be used to differentiate scrub typhus and dengue within a few hours of presentation to the hospital.
Keywords: Acute undifferentiated febrile illness, clinical score to differentiate scrub typhus and dengue score, dengue fever, scrub typhus, validity
|How to cite this article:|
Mutyala SK, Mitra S, Abhilash KP, Jayaseelan V. Validation of a clinical score to differentiate scrub typhus and dengue. Curr Med Issues 2017;15:121-4
|How to cite this URL:|
Mutyala SK, Mitra S, Abhilash KP, Jayaseelan V. Validation of a clinical score to differentiate scrub typhus and dengue. Curr Med Issues [serial online] 2017 [cited 2020 Jul 7];15:121-4. Available from: http://www.cmijournal.org/text.asp?2017/15/2/121/206512
| Introduction|| |
The presentation of acute undifferentiated febrile illness (AUFI) is seasonal and peaks during the rainy season. Nonspecific symptoms include fever, generalized myalgia, and fatigue. Scrub typhus and dengue are the most commonly encountered causes of AUFI in many emergency departments (EDs) of South India. Dengue fever is an arthropod-borne disease and is endemic in many parts of India during the monsoon season. Scrub typhus is a zoonotic infection and is widely prevalent in areas with heavy monsoon and agrarian way of life. In many areas of developing countries where diagnostic facilities are limited, etiologies of AUFI remain largely unknown. Physicians often diagnose patients presumptively based on clinical features and start empiric antibiotics. Delay in diagnosis and initiation of appropriate antibiotic therapy can be associated with significant mortality.,,, A study done in 2012 in the same South Indian hospital showed that scrub typhus and dengue account for 66.5% of all AUFIs. Diagnostic tests for scrub typhus and dengue have many limitations such as cost, availability in smaller centers, and reliability. Hence, Mitra et al. proposed a clinical score to differentiate scrub typhus and dengue (CSSD score). This scoring system included six easily available variables (SpO2, hemoglobin, total white blood cell [WBC] count, serum glutamic oxaloacetic transaminase [SGOT] level, serum bilirubin, and sensorium). The aim of our study is to validate the diagnostic performance of the CSSD score in our ED.
| Materials and Methods|| |
This retrospective observational study was conducted in Christian Medical College, Vellore, a 2700-bed tertiary care hospital in Tamil Nadu, South India, between September 2014 and December 2014. All adult patients more than 15 years of age presenting with an AUFI lasting between 3 and 14 days with no evident focus of infection following initial clinical evaluation were screened. Patients with confirmed scrub typhus and dengue were included in the analysis.
Details of history and results of a thorough physical examination were entered on a standard data collection sheet. The routine baseline investigations that were sent for all patients included complete blood count analysis, serum electrolytes, and liver and renal function tests. The commercial enzyme-linked immunosorbent assay (ELISA) tests performed were Dengue IgM ELISA (Panbio ®; Dengue Duo Cassette) and Scrub typhus IgM ELISA (InBios International, Inc., Seattle, WA, USA). The result was interpreted according to the manufacturer's instruction as positive, equivocal, or negative. These serological tests were done on or after the 7th day of fever.
- Scrub typhus: Eschar + Scrub IgM ELISA positive or scrub IgM ELISA positive with other serologies and blood culture negative
- Dengue: Clinical features of dengue with dengue IgM positive and other serologies and blood culture negative
- CSSD score: as shown in [Table 1].
The six variables needed for the CSSD score were obtained and the score was calculated. The patients were presumptively diagnosed as having either scrub typhus or dengue. After confirmation of the diagnosis based on the serological tests and results of blood culture, the patients were finally classified as having either scrub typhus or dengue fever.
Statistical analysis was performed using SPSS software for Windows (SPSS Inc., Released 2007, version 16.0, Chicago, IL, USA). Continuous variables are presented as mean (standard deviation) or as median (range) depending on the distribution of the data. Categorical and nominal variables are presented as percentages. Chi-square test or Fisher's exact test was used to compare dichotomous variables and t-test or Mann–Whitney test was used for continuous variables as appropriate. A two-sided P< 0.05 was considered statistically significant. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated separately for both dengue and scrub typhus patients.
This study was approved by the Institutional Review Board (IRB Minimum No. 9626 dated September 01, 2015), and patient confidentiality was maintained using unique identifiers and by password-protected data entry software with restricted users.
| Results|| |
During the study period, 134 confirmed cases of scrub typhus and dengue were included in the analysis, of which 68 were scrub typhus and 66 were dengue. A male predominance was seen in dengue (60.6%), whereas females comprised the majority in scrub typhus (58.8%). The mean time to presentation was longer in scrub typhus (7.56 ± 3.2) days compared to dengue (4.43 ± 2.16). A characteristic eschar was seen in 64.7% of patients with scrub typhus. The baseline characteristics are shown in [Table 2]. Features of systemic inflammatory response syndrome were seen in 71.2% of patients with dengue and in 92.6% of patients with scrub typhus. A maximum number of dengue cases were recorded in the month of October (39.4%) and minimum in the month of December (7.6%). Similarly, scrub typhus had a peak incidence in November (45.6%) [Figure 1]. The laboratory investigations are shown in [Table 3].
Among 68 confirmed cases of scrub typhus, 32 patients have CSSD score <13, favoring scrub typhus. Among 66 confirmed cases of dengue, 64 patients have CSSD score ≥13, favoring dengue. CSSD score has high specificity (97%) and positive predictive value (94%) for scrub typhus patients. CSSD score has high sensitivity (97%) and negative predictive value (94%) for dengue patients [Table 4].
|Table 4: Diagnostic performance of clinical score to differentiate scrub typhus and dengue|
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| Discussion|| |
The aim of our study was to validate the already proposed CSSD score to differentiate scrub typhus and dengue at initial presentation to the ED. Our study showed the CSSD to have high specificity (97%) and positive predictive value (94%) for scrub typhus patients and a high sensitivity (97%) and negative predictive value (94%) for dengue patients.
CSSD is a clinical scoring system derived after trying five models using seven variables (SpO2, hemoglobin, total WBC, SGOT level, serum bilirubin, sensorium, and age). Model 5 was determined to be the best and uses six variables (all excluding age). A few studies to identify distinguishing characteristics between the two infections have also been done in the past, but the scoring system was the first of its kind. Among the variables, higher hemoglobin/hematocrit and leukopenia are strongly associated with dengue. Low saturation due to respiratory system involvement, leukocytosis, altered sensorium, jaundice, and transaminitis is more frequently associated with scrub typhus. These associations have been consistent findings in studies done on these two infections. These basic blood investigations are widely available and take only a few hours to be done. Hence, it makes practical sense in using these variables to differentiate scrub typhus and dengue.
Two variables that were not included in the CSSD and that we found to be significant were mean age and duration of illness. In our study, the mean age among dengue patients (31.5 ± 12.1 years) was lesser than the mean age for scrub typhus (47 ± 15.2 years). This finding is consistent with studies on these two infections from other places., The mean duration of illness depends on the time taken by the participants to seek medical attention and also the incubation period. We found the mean duration of fever to be significantly shorter in dengue fever (4.43 ± 2.16) when compared to scrub typhus (7.56 ± 3.2). Previous studies done by Chang et al. in Taiwan and Tantawichien in Bangkok showed a mean duration of fever of 4.92 days and 5.2 days, respectively, among dengue patients., Studies done in South India showed a mean duration of fever of 8–8.5 days among patients with scrub typhus., These two variables may perhaps be useful in distinguishing the two infections in future studies used to design scoring systems.
An eschar is a pathognomonic sign of scrub typhus infection and the most useful diagnostic clue in patients with acute febrile illness in areas endemic for scrub typhus and therefore should be thoroughly examined for its presence, especially over the covered areas such as the groin, genitalia, infra-mammary area, and axilla. However, it is quite frequently missed on a routine physical examination. The eschar detection rate is very variable ranging from 14.5% to 67%.,, The detection rates are very high in the orient (Japan and Korea) which may be due to the racial differences in the skin color aiding in easy identification., In our study, the detection rate of eschar was found to be 64.7% which is much higher when compared to previous studies.,,, This is probably due to increasing awareness of the disease and vigilance in searching for this vital diagnostic feature. The presence of an eschar is a characteristic feature of patients with scrub typhus and helps in differentiating from cases of dengue fever.
The retrospective nature of our study was a major limitation. Since serological tests could not be done prospectively, we had to rely on the confirmation of the cases by the admitting unit to include in our study. Prospective validation of the scoring system would shed more light on the usefulness of the CSSD.
| Conclusion|| |
The CSSD is a simple and inexpensive score that can be done rapidly at initial presentation of the patient to the ED. It has a high specificity and positive predictive value for scrub typhus and high sensitivity and negative predictive value for dengue and can be used to differentiate scrub typhus and dengue within a few hours of presentation to the hospital.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]