Use of Typhidot in the Diagnosis and Treatment of Typhoid Fever*

Transcription

1 Use of Typhidot in the Diagnosis and Treatment of Typhoid Fever* Adrian C. Peña, M.D.** and Edwin Pasumbal*** (*Paper presented in part during the 2 nd Annual Convention of the Philippine College of Physicians, Shangri-la EDSA, May 7-0, 2002; **Associate Professor and Chief, Section of Infectious Diseases, Department of Medicine, University of the East-Ramon Magsaysay Memorial Medical Center, Aurora Boulevard, Quezon City and Consultant, Section of Infectious Diseases, Department of Medicine, St. Luke s Medical Center, E. Rodriguez Avenue, Quezon City; ***Fellow, Section of Infectious Diseases, Department of Medicine, St. Luke s Medical Center, E. Rodriguez Avenue, Quezon City ABSTRACT A retrospective study was conducted at the St. Luke s Medical Center to determine how physicians utilize the typhidot test and how the results affect their medical intervention and final diagnosis. All requests for typhidot test and results from January 999 to December 2000 were obtained and the charts of the patients who were 8 years old and above were reviewed. The patients were grouped into 4 based on the results of the typhidot tests: Group I, IgM+/IgG+; Group II, IgM+/IgG-; Group III, IgM -/IgG+; and Group IV, IgM -/IgG-. The following data were also reviewed: blood culture requests and results, antibiotic and other medical interventions and final diagnoses. A total of 88 patients, 5 males and 7 females had requests for typhidot test. Only 44 (50%) of these patients had concomitant blood culture requests and in only were organisms isolated. Salmonella typhi grew out in / and /2 blood culture requests in Groups I ( patients) and II ( patients). S. aureus grew out in /4 in Group IV (77 patients). All patients in Groups I and II were treated as typhoid fever consistent with the interpretation of the presence of IgM with or without the presence of IgG and were treated correctly. In Group III (5 patients) where only IgG was present, 4 patients were given a final diagnosis of enteric/typhoid fever with one patient being diagnosed with concomitant amoebic colitis. The antibiotics given for this patient, however, did not contain an anti-typhoid drug. The 5 th patient had a final diagnosis of acute appendicitis and managed as such. Despite the absence of both IgG and IgM and absence of growth in 8 blood cultures, 0 of the 77 patients in this group were still treated as enteric/typhoid fever based on clinical grounds. The rest were given non-typhoidal final diagnoses with majority being given adequate treatment consistent with their diagnoses. It is therefore recommended that the typhidot test should not be used as a screening test for all fevers and requests should be limited to fevers where there is a high clinical suspicion of enteric/typhoid fever. [Phil J Microbiol Infect Dis 2002; (4):6-64] Keywords: dot EIA, enteric fever, typhidot, typhoid fever, Salmonella typhi INTRODUCTION Typhoid Fever is a systemic infection caused by Salmonella typhi. It is endemic in developing countries and is a major cause of morbidity and mortality. While blood culture is the gold standard in the diagnosis of the disease, it is hampered by low sensitivity, high specificity and delayed results that come out in 4-7 days. This has led to the development of rapid diagnostic tests, two of which - widal test and typhidot (dot EIA) test - are currently available in the Philippines. The widal test demonstrates the presence of somatic (O) and flagellar (H) antigens of S. typhi and S. paratyphi A, B, and C. However, single titers are non-diagnostic and paired titers one week apart are necessary for confirmation of a clinical diagnosis. Moreover, 55% of healthy Filipinos have detectable O and H agglutinins to Salmonellae. The Philippine Society for Microbiology and Infectious Diseases came out with a position paper in 99 on the use of widal test in the diagnosis of enteric/ typhoid fever. In the position paper, it stated that:. blood and/or bone marrow culture are the diagnostic tests for confirmation of typhoid fever; 2. a single test in an endemic area is of no value and it should not be used as a screening test for asymptomatic individuals;. a negative test does not rule out

2 typhoid fever in patients with signs and symptoms of the disease; and it should not be used as a basis for deciding duration of treatment. 2 The typhidot is a dot enzyme immunoassay utilizing a 50 kd outer membrane protein which is specific for Salmonella typhi infection. The results are interpreted thus: IgM+/IgG+ or IgM+/IgG-, S. typhi infection present; IgM-/IgG+, convalescence or past S. typhi infection; IgM- /IgG-, no S. typhi infection. With the high specificity, reliability and rapidity of the test, the dot EIA technique was envisioned to provide a simple and useful method for the serodiagnosis of typhoid fever. An added advantage of the typhidot test over widal test is that the results were deemed reliable even if a single serum specimen is used for the test. There have been two studies to validate the use of the typhidot test in diagnosing typhoid fever among Filipinos. The results of the studies showed variable sensitivity, low specificity, low positive and variable negative predictive values and high false positive rates. 4,5 Since the introduction of the typhidot test in the Philippines, clin ical experience has shown an increase in requests for this diagnostic modality. In fact, it has replaced the widal test as the diagnostic method of choice for typhoid/enteric fever. It is the objective of this study to determine how physicians utilize the typhidot test and how the results affect their medical intervention and final diagnosis. MATERIALS AND METHODS This is a retrospective study. The logbook of the Microbiology Section of the Institute of Pathology of St. Luke s Medical Center was reviewed. All requests for typhidot test and results from January 999 to December 2000 were obtained. The charts of the patients who were 8 years old and above were reviewed. The patients were grouped into 4 based on the results of the typhidot tests: Group I, IgM+/IgG+; Group II, IgM+/ IgG-; Group III, IgM-/IgG+; and Group IV, IgM-/IgG-. The following data were also reviewed: blood culture requests and results, antibiotic intervention and final diagnosis. RESULTS A total of 88 patients, 5 males and 7 females had requests for typhidot test. Only 44 (50%) of these patients had concomitant blood culture requests. Table shows the groupings of the patients and blood cultures requested. Table. The patients groups and blood culture requests Group No % Blood culture requests % I II III IV %.4% 5.7% 87.5% Of the blood cultures requested, had positive isolates. Salmonella typhi grew out in / and /2 blood culture requests in Groups I and II. S. aureus grew out in /4 blood culture requests in Group IV. All other blood cultures requested had no growth. All patients in Groups I and II were treated as typhoid fever consistent with the interpretation of the presence of IgM with or without the presence of IgG. In Group III where only IgG was present, 4 patients were given a final diagnosis of enteric/typhoid fever with one patient being diagnosed with concomitant amebic colitis. The antibiotics given for this patient, however, did not contain an anti-typhoid drug. The 5 th patient had a final diagnosis of acute appendicitis and managed as such (Table 2). The final diagnoses and management of Group IV patients are shown in Table. Despite the absence of both IgG and IgM and absence of growth in

3 8 blood cultures, 0 of the 77 patients in this group were still treated as enteric/typhoid fever. The rest were given non-typhoidal final diagnoses (Table 4). Table 2. Final diagnosis and treatment of Group III patients Final diagnosis No. % Treatment Enteric/Typhoid Fever Typhoid Fever + Amebic colitis Acute appendicitis Ceftriaxone; Chloramphenicol; Ciprofloxacin Secnidazole + Doxycycline Appendectomy + Ciprofloxacin Table. Final diagnosis and treatment of Group IV patients (N=77) Final diagnosis No. % Treatment Enteric/Typhoid Fever Nontyphoidal 0* 67 % 87% Amoxicillin; Quinolones See table 4 *Concomitant PTB in patient; treated accordingly Table 4. Final diagnosis and treatment of Group IV non-typhoidal patients (N=67) Final Diagnosis No. % Treatment Systemic viral infection 2 4. Dengue hemorrhagic fever Urinary tract infection Acute gastroenteritis Pneumonia Acute sinusitis Acute appendicitis Cellulitis** German measles Hemorrhoids Hepatic cyst Infected wound, foot Malaria Mumps with orchitis Systemic lupus erythematosus TB meningitis Typhus fever Upper respiratory tract Infection *Concomitant amebiasis was diagnosed in one patient **S. aureus grew on blood culture DISCUSSION Dirithromycin (2); Metronidazole ()*; Ciprofloxacin (); Supportive (7) Ciprorofloxacin (); Supportive () Cefuroxime (); Ciprofloxacin (2); Ofloxacin (2); Co-amoxiclav () Ciprofloxacin (); Metronidazole (2); Ofloxacin () Ceftazidime; Norfloxacin; Cefuroxime Cotrimoxazole Ofloxacin + Metronidazole + surgery Co-amoxiclav Supportive Supportive Ciprofloxacin Co-amoxiclav Quinine Pefloxacin Steroids Quadruple Anti-TB drugs Doxycycline Azithromycin A nitrocellulose membrane strip dotted with a specific 50 kda outer membrane protein of Salmonella typhi was applied for the serodiagnosis of typhoid fever. The detection of specific IgM and IgG antibodies in typhoid patients suggest either recent or current infection. This dot EIA technique, typhidot test, provides a simple and useful method for the serodiagnosis of typhoid using a single serum specimen. Physicians, however, will have to be aware that there is the risk of false positive tests. The group that developed this dot EIA test in fact recommended this caveat. Their study showed a mean persistence of IgM dot EIA positivity of 2.6 months (95% confidence interval = months) and that of IgG was 5.4 months ( months) in children treated for typhoid fever

4 and that, therefore, positive results should be interpreted with caution. 6 How this would relate to adults is unknown at this time due to absence of studies in the adult population. A study done at Capitol Medical Center involving 69 patients who were 6-60 years of age with fever less than or equal to 4 days was conducted to determine the reliability of the typhidot test in the diagnosis of typhoid fever. Included in the study were patients with clinical manifestations suggestive of typhoid fever, no history of immunization in the recent past, were immunocompetent and had both blood cultures and typhidot tests. The result of their study showed a sensitivity of 9%, specificity of 00% and a negative predictive value (NPV) of 9% for IgM+ positive patients with blood culture positive for S. typhi and a sensitivity of 79%, specificity of 00% and NPV of 8% for IgM+ patients with negative blood cultures. The sensitivity of IgG was 7%, specificity was 6%, and NPV was 22.4% for culture positive patients and 82%, 7% and 68% for culture negative patients. Moreover, the IgG had a false positive rate of 6%. A review showed an error in excluding IgM + but culture negative patients in the computation for the validity of IgM and IgG and therefore reduced the study population from 69 to. A re-computation showed that for IgM, the sensitivity remained at 9% but the specificity was reduced to 6% instead of 00%, the positive predictive value (PPV) was 54% and the NPV became 94%. On the other hand, for IgG, the sensitivity was 7%, the specificity was even lower at 27% (from 6%), the PPV was % and the NPV was 67% (Tables 5 and 6). Table 5. Validity of typhidot IgM Blood Culture + - Total IgM + IgM Total Sensitivity = 9%; Specificity = 6%; PPV = 54%; NPV = 94% Table 6. Validity of typhidot IgG Blood Culture + - Total IgG + IgG Total Sensitivity = 7%; Specificity = 27%; PPV = %; NPV = 67% The study done by Membrebe and Chua 4 on the clinical utility of typhidot in the diagnosis of typhoid fever in 85 patients showed the following results: sensitivity of 72%, specificity of 52%, PPV of %, NPV of 86%. On the basis of the blood culture results, the IgM had a high false positive rate of 68.6%. An analysis of 0 non-typhoid fever cases showed that 46 (45% false positive rate) had IgM positive tests with systemic viral infections making up the majority with cases (67.4%). Despite the variable sensitivity, very low specificity and positive predictive values, we have seen typhidot tests being requested at the expense of the gold standard, blood cultures. This is shown in the low 50% requests for blood cultures in our study. A review of the patients charts in groups I and II showed clinical histories and physical examination findings compatible with typhoid fever. These patients were treated correctly with anti-typhoid antibiotics. In group III, one patient given a final diagnosis of typhoid fever with concomitant amebiasis was treated only for the latter condition with secnidazole and doxycycline. It appeared that the attending physician actually doubted the results of the typhidot test, in which

5 case, the final diagnosis should have been written down as recent or past typhoid fever and amebiasis. The fifth patient in group III was eventually diagnosed as appendicitis, which had an atypical presentation. In this case, the attending completely ignored the typhidot test. Of the ten patients in group IV given a final diagnosis of enteric/typhoid fever, 8 had negative blood cultures and 2 had no blood culture requests. These patients were treated on clinical grounds. Analyzing the non-typhoidal patients, only the 2 SVI patients, 4 dengue fever patients and typhus fever patient would have manifestations that can be confused with enteric/typhoid fever. The typical rash and thrombocytopenia associated with dengue should have alerted the attending physicians that typhidot tests were not indicated. It is reassuring, however, that majority of the patients were given adequate management [supportive in SVI (7/2, 74%) and DF (/4, 9%); doxycycline in typhus fever]. Looking at the rest of the 29 patients in the non-typhoidal group, the diagnoses were so obvious that there was really no reason to request for typhidot tests. The only consola tion is that these patients were treated accordingly with respect to their eventual final diagnosis. CONCLUSION The typhidot test in our local studies showed variable sensitivity, very low specificity and positive predictive values and high false positive rates. Despite these rates, it appears that the typhidot test has replaced the widal test as a screening test for all patients with fever. It is therefore recommended that the typhidot test should not be used as a screening test for all fevers and requests should be limited to fevers where there is a high clinical suspicion of enteric/typhoid fever. REFERENCES. Basaca-Sevilla V, Pastrana EP, Cross JH, Sevilla JS, Balagot RG. The significance of the Widal Tests. Phil J Microbiol Infect Dis 979; 8: Tupasi TE, Lucas Aquino R, Mendoza MT, Tuazon CU, Lolekha S. Clinical application of the widal test. Phil J Microbiol Infect Dis 99; 20: Ismail AB, Kader ZSA, Ong KH. Dot enzyme immunosorbent assay for the serodiagnosis of typhoid fever. SEA J Trop Med Publ Health 99; 22: Collantes E, Velmonte MA. The validity of the typhidot test in diagnosing typhoid fever among Filipinos. Phil J Microbiol Infect Dis 997; 20: Membrebe FA, Chua JA. The Clinical Utility of Typhidot in the Diagnosis of Typhoid Fever. Phil J Microbiol Infect Dis 999; 28: Choo KE, Davis TM, Ismail A, Ong KH. Longevity of antibody responses to a Salmonella typhi-specific outer membrane protein: Interpretation of a dot enzyme immunosorbent assay in an area of high typhoid fever endemicity. Am J Trop Med Hyg 997 Dec;57(6):656-9.