1. RESULTS AND DISCUSSION
Poster Board Number: D-718
Control number 1950
All India Institute of Medical Sciences, New Delhi
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Scrub typhus in North India : A prospective analysis of
clinical epidemiology and evaluation of laboratory methods for diagnosis
Nitin Gupta*1,R Chaudhry1, AB Dey2, SK Kabra3, R Lodha3, BR Mirdha1, BK Das1, V Sreenivas4
1Department of Microbiology, 2Department of Geriatric Medicine, 3Department of Paediatrics,
4Department of Biostatistics, All India Institute of Medical Sciences, New Delhi
Evaluation of methods for diagnosis of Scrub typhus
IgM ELISA:
A set of 40 sera samples collected from healthy volunteers from New Delhi were used to establish region specific cutoff for IgM ELISA. The cut off was calculated as mean OD(0.332) + 3SD (0.169)
The cut off calculated was 0.839
Of the 25 IFA positive sera, 23 were positive while 2 of the 137 IFA negative sera were positive.
The sensitivity & specificity were 92% & 98.5% respectively
Rapid Flow Assay (IgM):
Of the 25 IFA positive sera, 29 were positive while none of the 137 IFA negative sera was positive
The sensitivity & specificity were calculated as 76% & 100% respectively
Nested PCR:
Of the 25 IFA positive samples, 10 were positive while none of the 137 IFA negative samples were positive
The sensitivity & specificity were calculated as 40% & 100% respectively.
The sensitivity of PCR was low as most samples were sent long after the febrile illness started. By this time most patients would have already received antibiotic therapy2 or they would no longer be in the stage of bacteremia
INTRODUCTION
Scrub Typhus-A rickettsial disease caused by the bite of larval stage of trombiculid mite
Most reports in India are from the Southern peninsula, and Sub-himalayan region
Classical case description includes Fever, lymphadenopathy, rash and eschar
Serology is the mainstay in diagnosis and immunofluoroscence assay(IFA) is considered as the gold standard, however IFA has its limitations
There is a need for evaluation of other methods for detection
AIMS AND OBJECTIVES
Evaluation of the clinical epidemiology and laboratory parameters of patients diagnosed with scrub typhus
Evaluation of immunodiagnostic and molecular methods with respect to IFA for detection in patients of Scrub typhus in New Delhi
MATERIALS AND METHODS
A total of 162 patients of all age groups attending AIIMS clinics with clinically suspected Scrub typhus over a period of 18 months (October 2013 to March 2015) were taken
Complete history and examination along with relevant laboratory investigations were performed
Serum samples obtained from the patient were subjected to IFA for IgM
Serum samples were also subjected to IgM ELISA & Rapid Flow Assay (for IgM) for Scrub typhus
A nested PCR assay was performed on whole blood samples to detect a 483 bp segment of 56 k Da gene using conditions described by Furuya et al.1
Positive samples were subjected to IgM ELISA for Leptospira to look for co-infection
Parameters
IgM ELISA
RFA
IFA
Turn around time
2hrs
5 min
1.5 hrs
Minimum no. of samples for one test 5 1 8
Instruments required
Incubator
spectrophotometer
none
Incubator, fluorescence microscope
Technical expertise
required
Not required
Cost per sample
Rs 450
Rs 240
Rs 625
RESULTS AND DISCUSSION
A total of 15.43% (25 out of 162) of suspected patients were positive for IgM antibodies by immunofluoroscence assay
There was a definite seasonal clustering with 80% of the Scrub typhus cases reporting in the months of October to December
The younger age group (11-30 years) was more frequently affected (14/25, 56%). Male: Female ratio was 1.27:1
Diagnostic test
Sensitivity
Specificity
PPV
NPV
IgM ELISA
92%
98.5%
RFA
76%
100%
95.8%
Nested PCR
40%
90.13%
Co-infection with Leptospirosis
Scrub typhus and Leptospirosis co-infection has been reported worldwide and also from India in recent past
All the 25 IFA positive samples were subjected to IgM ELISA for Leptospirosis
9 samples were positive for IgM antibodies against Leptospira also
The 7 samples that were positive for both were further analysed to confirm whether they were actual cases of co- infection
Only 1 patient was confirmed as a case of co-infetion with PCR assays positive for both scrub typhus and leptospirosis
Clinical and laboratory profile of patients with scrub typhus
SUMMARY AND CONCLUSIONS
Clinical features
Numbers
Percentage
Fever
25/25
100%
Rash
7/25
28 %
Lymphadenopathy
3/25
12 %
Eschar
Hepatomegaly
12/25
48 %
Splenomegaly
5/25
20 %
Pulmonary
17/25
68 %
CNS
4/25
16 %
CVS
6/25
24 %
Laboratory findings
Numbers
Percentage
Leucocytosis
11/25
44%
Thrombocytopenia
10/25
40%
Transaminitis
13/25
52%
Scrub typhus is an under reported infectious disease from this part of the country
The typical manifestations like rash, lymphadenopathy and eschar are rare
Patients with fever, pulmonary manifestations and/ or deranged LFT presenting in the months of August to December should be evaluated for Scrub typhus
Even though molecular techniques like PCR are highly specific, their low sensitivity makes them an unsuitable alternative for immunodiagnostic tests. Their use as an adjunct to immunodiagnosis is desirable wherever possible
REFERENCES
1. Furuya Y, Yoshida Y, Katayama T et al. Specific amplification of Rickettsia tsutsugamushi DNA from clinical specimens by polymerase chain reaction. J Clin Microbiol.1993; 29:
2. Kim DM, Byun JN. Effects of antibiotic treatment on the results of nested PCRs for scrub typhus. J Clin Microbio Oct; 46(10).
The prevalence of classical mainfestations like lymphadenopathy and eschar were found to be low while pulmonary manifestations and hepatomegaly were fairly common