Indan Journal of Medical Research Indan Journal of Medical Research Indan Journal of Medical Research Indan Journal of Medical Research
  Home About us Editorial board Search Ahead of print Current issue Archives Submit article Instructions Subscribe Contacts Login  
  Home Print this page Email this page Small font sizeDefault font sizeIncrease font size Users Online: 1778       

   Table of Contents      
ORIGINAL ARTICLE
Year : 2017  |  Volume : 146  |  Issue : 3  |  Page : 386-391

Unreliability of three commercial Coxiella burnetii phase II IgM ELISA kits for the seroscreening of acute Q fever in human cases


1 Department of Microbiology, Mahatma Gandhi Medical College & Research Institute, Puducherry, India
2 Department of General Medicine, Indira Gandhi Government General Hospital & Post Graduate Institute, Puducherry, India
3 Department of Paediatrics, Mahatma Gandhi Medical College & Research Institute, Puducherry, India
4 Department of Microbiology, Indira Gandhi Government General Hospital & Post Graduate Institute, Puducherry, India

Date of Submission20-Nov-2015
Date of Web Publication18-Jan-2018

Correspondence Address:
Dr Selvaraj Stephen
Department of Microbiology, Mahatma Gandhi Medical College & Research Institute, Pondy-Cuddalore Main Road, Pillaiyarkuppam, Puducherry 607 402
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijmr.IJMR_1815_15

Rights and Permissions
   Abstract 

Background & objectives: Seroprevalence of Q fever (QF) caused by Coxiella burnetii has been reported from different parts of India. Usually serological/molecular tests are employed for detection of infection. The present study was undertaken to verify the validity of three different QF phase II IgM ELISA kits for acute QF diagnosis by comparing with the gold standard indirect fluorescent antibody assay (IFA).
Methods: Fifty eight serum samples collected from 42 patients (26 patients provided acute sample only and 16 both acute and convalescent samples) which were examined by all three commercial kits, were cross-checked with QF Phase II IgM IFA for confirmation.
Results: Eleven patients were positive for C. burnetii antibodies by IFA in acute and/or convalescent serum samples. Taking IFA as a reference, percentages of sensitivity, specificity, positive predictive value and negative predictive value for Virion-Serion/Vircell/NovaTec were 36.36, 61.29, 25.00, 73.08; 81.82, 35.48, 31.03, 84.62 and 100, 25.81, 32.35, 100 per cent, respectively.
Interpretation & conclusions: The three different ELISA kits exhibited poor agreement amongst them and unacceptable level of false positivity. IFA remains to be the only option for diagnosing acute QF. Discrepancy between the clinical findings and IFA/ELISA results needs confirmation by C. burnetii DNA detection in real-time polymerase chain reaction.

Keywords: Coxiella burnetii - ELISA false positivity - indirect fluorescent antibody assay - Q fever


How to cite this article:
Stephen S, Ambroise S, Pradeep J, Gunasekaran D, Sangeetha B, Sarangapani K. Unreliability of three commercial Coxiella burnetii phase II IgM ELISA kits for the seroscreening of acute Q fever in human cases. Indian J Med Res 2017;146:386-91

How to cite this URL:
Stephen S, Ambroise S, Pradeep J, Gunasekaran D, Sangeetha B, Sarangapani K. Unreliability of three commercial Coxiella burnetii phase II IgM ELISA kits for the seroscreening of acute Q fever in human cases. Indian J Med Res [serial online] 2017 [cited 2020 Feb 23];146:386-91. Available from: http://www.ijmr.org.in/text.asp?2017/146/3/386/223632

Q fever (QF) in humans and animals caused by Coxiella burnetii has been reported throughout the world[1]. Reports of coxiellosis in different countries have raised the awareness level of Q fever [2],[3],[4]. Slaughterhouse workers are at high risk and pregnant women are at low risk to contract QF[5],[6]. During 1979-1986, country-wide serological surveys established the prevalence of QF in India [7],[8],[9],[10], with cases of human abortions, endocarditis and neonatal septicaemia reported subsequently [11],[12],[13].

C. burnetii occurs in nature in phase I in animals and arthropods. In vitro passage in yolk sac or transmission to humans leads to conversion to phase II. Phase II IgM/IgG antibodies are most prevalent during acute infection and phase I IgG antibodies are indicative of chronic infection to C. burnetii[2],[3]. In its acute form, QF manifests itself as subclinical infection, febrile illness resembling flu, atypical pneumonia, pneumonitis, hepatitis, meningitis and infrequently as chronic fatigue syndrome with prolonged fatigue, arthralgia, myalgia, muscle fasciculation, blurred vision, sweats and enlarged painful lymph nodes[2]. Endocarditis is the most common manifestation of chronic QF[1],[2],[3],[12]. The causative organism C. burnetii, an intracellular Gram-negative bacterium does not grow on cell-free medium and can only be cultivated in the laboratory animals (guinea pigs)/yolk sacs of developing chick embryos/tissue cultures. This being a Category B/Bio-safety level 3 pathogen with potential for bioterrorism[11], isolation attempts are made only in rickettsial research/reference laboratories. Hence, culture is not an option in infected cases. Therefore, serological/molecular tests are employed for diagnosing the infection. Conventionally, serological tests such as Luoto's capillary agglutination test[14], Fiset's micro-agglutination test[15], complement fixation test[2] and immunoperoxidase test[1] were used. However, only ELISA and indirect fluorescent antibody assay (IFA) are used in practice in several countries[1],[2],[3],[4],[5],[6],[16],[17],[18],[19],[20],[21]. Serological diagnostic kits such as IFA are expensive. For detection of C. burnetii, DNA, polymerase chain reaction (PCR), quantitative PCR (qPCR)[22],[23],[24], and a new test, loop-mediated isothermal amplification (LAMP)[25] have been employed. LAMP/PCR/qPCR kits need to be imported and standardized. Running real-time PCR is not feasible in many laboratories due to the exorbitant cost of the machine. Therefore, the objective of this study was to verify the reliability of three commercial Coxiella burnetii Phase II IgM ELISA kits available in India for acute QF diagnosis, by comparing with phase II IgM IFA.


   Material & Methods Top


This study was conducted during April 2013-January 2015 in the department of Microbiology and Paediatrics, Mahatma Gandhi Medical College and Research Institute (MGMC and RI), and departments of General Medicine and Microbiology, Indira Gandhi Government General Hospital and Post-Graduate Institute, Puducherry, India. Majority of the patients were from rural areas of Puducherry and surrounding Cuddalore, Neyveli, Virudhachalam and Villupuram districts of Tamil Nadu. The Institutional Human Ethical Committee of MGMC and RI approved this research project. Informed written consent was obtained from adult patients and parents/guardians of children, before collection of blood samples. Inclusion criteria were high-grade fever with or without chills and rigour; fever with either pneumonia/pneumonitis, or with rash/hepatosplenomegaly/jaundice/lymphadenopathy/thrombocytopaenia, or with constitutional symptoms such as malaise, myalgia, nausea and vomiting. Exclusion criteria were fever due to urinary tract infection/malaria/enteric fever; culture-positive bacterial pneumonia; patients with other bloodstream infections; bleeding disorders and fever of more than four weeks duration (pulmonary tuberculosis).

Sample size calculation was made considering the national average prevalence 16 per cent for human QF during the past six decades [7],[8],[9]. The power of the study was 74 per cent. Of the 470 patients registered in the study, only 310 provided both acute and convalescent blood samples. The remaining 160 patients did not turn up for the convalescent sample collection. Of the 310 patients, after excluding 35 lipaemic and haemolyzed samples, 275 samples were processed. Paired blood samples (5 ml) in sterile plastic plain tubes without anti-coagulants were collected from these 275 patients at 2-3 wk intervals, over a period of 22 months. All 275 patients could not be screened by QF Phase II IgM ELISA because of the unreliability of all three kits. Only 42 patients were finally tested by all three ELISA kits with the positivity in one/two/three kits. Because of discrepancy amongst these three kits, confirmation by phase II IFA IgM was carried out. Sixteen patients belonged to the first group (paired samples) and the remaining 26 patients in the second group (acute samples only) (total 58 serum samples).

ELISA for  Coxiella burnetii Scientific Name Search ntibody testing: Serum was separated, aliquoted and stored at −20°C till the time of testing. Three different ELISA kits were evaluated: (i) C. burnetii (QF) phase II IgM - ELISA, NovaTec, Immundiagnostica GmbH, Dietzenbach, Germany; (ii) C. burnetii phase II IgM - Virion/Serion, Immundiagnostica GmbH, Wurzburg, Germany; and (iii) C. burnetii ELISA phase II IgM - Vircell, Granada, Spain. Samples positive in one or more ELISA kits were cross-checked for confirmation by IFA.

The following biological positive controls collected from MGMC and RI were included: typhoid (Widal positive) (2), falciparum malaria (1), dengue (3) and rheumatoid arthritis (2). Biological negative controls include typhoid (5), leptospirosis (2), vivax malaria (1) and dengue (3). The tests were carried out strictly adhering to the technical instructions provided by the manufacturers of these three kits and as performed by earlier researchers[19],[21],[26],[27]. All three kits were coated with killed phase II C. burnetii antigen. Procedure and interpretation of the test results were more or less common for all three kits. Briefly, serum samples was diluted 1:100 for NovaTec and Virion/Serion but 1:20 for Vircell. Plates were incubated for 1 h±5 min at 37°C±1°C, followed by 3-5 washes with wash buffer and then aspiration. C. burnetii anti-IgM conjugate (100 μl) was added and incubated for 30-60 min at room temperature. After three washes and aspiration, 100 μl 3,3', 5, 5'-tetramethylbenzidine (TMB) substrate solution was dispensed into all wells and incubated for 15 min at room temperature in the dark. Stop solution (50-100 μl) was added to all wells and the plates were read within half an hour. Optical density (OD) readings were taken with the wavelength of 450/620 nm for NovaTec and Vircell but 405/620 nm for Virion/Serion using iMark Microplate Reader (Bio-Rad Laboratories Inc, Shinagawa-Ku, Tokyo, Japan).

Cut-off value calculation was similar for both NovaTec and Vircell kits. Antibody index=(Sample OD/Cut-off OD)×10. The samples with OD values above the cut-off 11 nephelometric turbidity unit were considered positive and those below the cut-off 9 were taken as negative. Borderline samples with cut-off 9-11 were tested in triplicate, while other samples were run in duplicate. For Virion/Serion, 10 per cent and above the cut-off value was taken as positive, whereas 10 per cent and below the cut-off was considered as negative.

Indirect fluorescent antibody assay (IFA): This test was carried out with QF IFA IgM Antibody kit (Fuller Laboratories, Fullerton, California, USA) which identified both phase I and phase II IgM antibodies against C. burnetii. Fifty eight serum samples from 42 patients which were screened by all three commercial ELISA kits, were taken up for this purpose. IFA was performed by adhering to the manufacturer's instructions and as reported by Hackert et al[21]. Patients' serum samples were initially diluted to 1:16 in IgM sample dilution buffer provided with the kit. After the final wash, the slides were dried, mounted with the mounting medium and read with ×400 magnification, at 390 nm using Primo Star iLED Fluorescent microscope (Carl Zeiss MicroImaging GmbH, Göttingen, Germany).

Statistical analysis: Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and their respective 95 per cent confidence intervals (CIs) were calculated considering QF IFA IgM as gold standard. For other parameters (Spearman's correlation and Kappa), statistical analysis was performed using IBM 2008 SPSS Statistics version 17.0 for Windows (SPSS Inc., Chicago, IL, USA). Chi-square test with Yates correction (Fisher's test) for small number of samples was performed for categorical data.


   Results Top


Clinical and laboratory findings of 275 patients recruited in the study are presented in [Table 1]. Of the 42 patients screened by all four serological tests for QF, 11 IFA-positive patients could be considered as presumptive QF cases. This included six children in the age group of 0-14 yr and five adults aged 15 yr and above (range 2 to 60 yr). Mean age was 20.19 ±17.9 and male/female ratio was 4:7. The highest percentage of seropositivity of 80.95 per cent (34/42) was shown by NovaTec ELISA kit followed by Vircell with 69.04 per cent (29/42) and Virion/Serion with 38.09 per cent (16/42). While comparing the results of QF phase II IgM ELISA and IFA, it was observed that of the 42 patients positive in one or more ELISA tests, only 11 were positive for phase II IgM in IFA [Table 2]. QF phase II IgM IFA titres ranged from 1:16 to 1:512 and QF phase I IgM IFA titres ranged from 1:16 to 1:32. Phase I and phase II IgM antibodies were seen in four patients. Sensitivity, specificity, PPV and NPV of the kits are presented in [Table 3]. Among the eight biological positive controls, one patient whose serum was positive in Widal test, was positive for both phase I and phase II QF IgM IFA with a titre of 1:32 each. The patient's serum was also positive for QF phase II IgM by all three ELISA kits. Eleven biological negative controls were negative in all four serological tests for QF.
Table 1: Clinical and laboratory findings of patients recruited in the study (n=275)

Click here to view
Table 2: Analysis of Q fever phase II IgM ELISA results against the ‘gold standard’ indirect fluorescent antibody (IFA) assay (n=42)

Click here to view
Table 3: Statistical analysis and comparison of three commercial ELISA kits with indirect fluorescent antibody (IFA) assay (n=42)

Click here to view



   Discussion Top


A significant difference was observed between children and adults regarding certain parameters; more adult patients had low platelet counts, increased liver enzymes and creatinine, headache, myalgia, chills and rigour, malaise and nausea. Hepatomegaly was seen in more number of children than adults. However, analysis of clinical findings and laboratory parameters of 11 QF IFA phase II IgM-positive cases did not reveal any significant difference between adults and children.

It is generally accepted that IFA is the gold standard for the serological diagnosis and confirmation of QF and other rickettsial diseases[1],[2],[3],[17],[19],[20],[21]. ELISA has also been considered sensitive, specific and useful in serological surveys[1],[2],[4],[5],[21]. According to Kantsø et al[26], Vircell QF phase II IgM ELISA kit had a sensitivity of 15 per cent and specificity of 94 per cent. As per our data, the percentage sensitivity and specificity for Vircell were 81.82 and 35.48 per cent, respectively. Meekelenkamp et al[20] compared the sensitivity and specificity of Focus IFA and Virion/Serion ELISA. The sensitivity of the IFA and ELISA tests was 100 and 85.7 per cent, with a specificity of 95.3 and 97.6 per cent, respectively. According to Herremans et al[18], the Focus IFA, ELISA (Virion/Serion) and Complement Fixation Assay (CFA, Virion/Serion) were all suitable serodiagnostic assays to diagnose acute QF, but the IFA remained an important tool in the follow up of patients and in identifying patients at risk for developing chronic QF. In their study, sensitivity and specificity of Virion/Serion Phase II IgM ELISA in diagnosing acute QF were found to be 60 and 100 per cent, respectively. As per our findings, the percentage sensitivity and specificity of Virion/Serion kit were 36.36 and 61.29, respectively. Medić et al[27] reported that of the 43 notified cases of acute QF, 37 were laboratory confirmed by NovaLisa Phase II IgM and/or IgG. The sensitivity and specificity of NovaTec ELISA kit were reported to be 100 and 88.4 per cent, respectively, in comparison to IFA in another study[28]. In our study, 100 per cent sensitivity but the lowest specificity of 25.81 per cent were found for NovaTec ELISA. Raven et al[29] drew the attention regarding the unpredictability of phase II IgM antibody positivity as a sole proof of acute QF and recommended to look for seroconversion of IgG, together with the clinical suspicion. A new algorithm for acute QF diagnosis[18],[21],[22],[23],[24],[30] emphasized the need to perform qPCR for confirmation. In resource-poor settings, the diagnosis may be limited to ELISA, and where facilities exist, IFA is carried out. In the initial phase of our research, a poor agreement in the seropositivity was observed amongst all three kits. Kappa values were not significant. Hence, the gold standard IFA (Phase II IgM) was the only option. As per the instructions provided by the manufacturers, IgM phase II IFA titres of ≥1:16 were taken as positive. The 11 patients had phase II IgM IFA titres ranging from 1:16 to 1:512. C. burnetii phase I IgM was seen together with phase II IgM in four patients.

The most commonly used means of confirming the diagnosis of acute QF is demonstration of a four-fold rise in phase II IgG by IFA between serum samples from the acute and convalescent phases taken 3-6 wk apart. Of the 16 patients for whom sufficient quantity of acute and convalescent serum samples were available for all the four tests, four-fold or more increase in titres in paired serum samples in QF phase II IgM IFA was demonstrated in only one patient, while seroconversion was observed in three cases. Six patients with only acute samples were positive for C. burnetii antibody in phase II IgM IFA. Eleven of the 42 patients (26.2%) could be identified as probable cases of acute QF, on the strength of positive QF phase II IgM in IFA.

This study had some limitations. QF PCR could not be performed since these kits were not available in India and any imported PCR kit needs to be first validated and standardized. QF phase II IgG IFA could not be carried out.

To conclude, disagreement in results of the three commercial C. burnetii phase II IgM ELISA kits was observed. Hence, their continued use for screening/serodiagnosis of acute QF needs re-thinking. QF IFA phase II IgG and IgM are to be carried out for paired serum samples, and in case of discrepancy, qPCR must be performed for confirmation.


   Acknowledgment Top


Funding by Indian Council of Medical Research (ICMR), New Delhi, for thisresearch project is acknowledged. Authors acknowledge the Chairman, Vice-Chancellor and Dean (Research, Post Graduate studies and Allied Health Sciences) of Mahatma Gandhi Medical College and Research Institute, Puducherry, for providing the facilities.

Conflicts of Interest: None.



 
   References Top

1.
Kovácová E, Kazár J. Rickettsial diseases and their serological diagnosis. Acta Virol 2002; 46 : 193-210.  Back to cited text no. 1
    
2.
Maurin M, Raoult D. Q fever. Clin Microbiol Rev 1999; 12 : 518-53.  Back to cited text no. 2
    
3.
McQuiston JH, Childs JE. Q fever in humans and animals in the United States. Vector Borne Zoonotic Dis 2002; 2 : 179-91.  Back to cited text no. 3
    
4.
El-Mahallawy HS, Kelly P, Zhang J, Yang Y, Wei L, Tian L, et al. Serological and molecular evidence of Coxiella burnetii in samples from humans and animals in China. Ann Agric Environ Med 2016; 23 : 87-91.  Back to cited text no. 4
    
5.
Esmaeili S, Naddaf SR, Pourhossein B, Hashemi Shahraki A, Bagheri Amiri F, Gouya MM, et al. Seroprevalence of brucellosis, leptospirosis, and Q fever among butchers and slaughterhouse workers in South-Eastern Iran. PLoS One 2016; 11 : e0144953.  Back to cited text no. 5
    
6.
Nielsen SY, Mølbak K, Henriksen TB, Krogfelt KA, Larsen CS, Villumsen S, et al. Adverse pregnancy outcomes and Coxiella burnetii antibodies in pregnant women, Denmark. Emerg Infect Dis 2014; 20 : 925-31.  Back to cited text no. 6
    
7.
Joshi MV, Padbidri VS, Rodrigues FM, Gupta NP. Prevalence of Coxiella burnetii infection among humans and domestic animals of Rajasthan State, India. J Hyg Epidemiol Microbiol Immunol 1979; 23 : 67-73.  Back to cited text no. 7
    
8.
Yadav MP, Sethi MS. Sero-epidemiological studies on coxiellosis in animals and man in the state of Uttar Pradesh and Delhi (India). Int J Zoonoses 1979; 6 : 67-74.  Back to cited text no. 8
    
9.
Stephen S, Achyutha Rao KN. Q fever in India: A review. J Indian Med Assoc 1980; 74 : 200-3.  Back to cited text no. 9
    
10.
Prasad BN, Chandiramani NK, Wagle A. Isolation of Coxiella burnetii from human sources. Int J Zoonoses 1986; 13 : 112-7.  Back to cited text no. 10
    
11.
Vaidya VM, Malik SVS, Kaur S, Kumar S, Barbuddhe SB. Comparison of PCR, IF, pathology and isolation for Q fever in humans with spontaneous abortion. J Clin Microbiol 2008; 46 : 2038-44.  Back to cited text no. 11
    
12.
Balakrishnan N, Menon T, Fournier PE, Raoult D. Bartonella quintana and Coxiella burnetii as causes of endocarditis, India. Emerg Infect Dis 2008; 14 : 1168-9.  Back to cited text no. 12
    
13.
Aarthi P, Bagyalakshmi R, Mohan KR, Krishna M, Nitin M, Madhavan HN, et al. First case series of emerging rickettsial neonatal sepsis identified by polymerase chain reaction-based deoxyribonucleic acid sequencing. Indian J Med Microbiol 2013; 31 : 343-8.  Back to cited text no. 13
    
14.
Luoto L. A capillary agglutination test for bovine Q fever. J Immunol 1953; 71 : 226-31.  Back to cited text no. 14
    
15.
Fiset P, Ormsbee RA, Silberman R, Peacock M, Spielman SH. A microagglutination technique for detection and measurement of rickettsial antibodies. Acta Virol 1969; 13 : 60-6.  Back to cited text no. 15
    
16.
La Scola B, Raoult D. Laboratory diagnosis of rickettsioses: Current approaches to diagnosis of old and new rickettsial diseases. J Clin Microbiol 1997; 35 : 2715-27.  Back to cited text no. 16
    
17.
Jager MM, Weers-Pothoff G, Hermans MH, Meekelenkamp JC, Schellekens JJ, Renders NH, et al. Evaluation of a diagnostic algorithm for acute Q fever in an outbreak setting. Clin Vaccine Immunol 2011; 18 : 963-8.  Back to cited text no. 17
    
18.
Herremans T, Hogema BM, Nabuurs M, Peeters M, Wegdam-Blans M, Schneeberger P, et al. Comparison of the performance of IFA, CFA, and ELISA assays for the serodiagnosis of acute Q fever by quality assessment. Diagn Microbiol Infect Dis 2013; 75 : 16-21.  Back to cited text no. 18
    
19.
Slabá K, Skultéty L, Toman R. Efficiency of various serological techniques for diagnosing Coxiella burnetii infection. Acta Virol 2005; 49 : 123-7.  Back to cited text no. 19
    
20.
Meekelenkamp JCE, Schneeberger PM, Wever PC, Leenders ACAP. Comparison of ELISA and indirect immunofluorescent antibody assay detecting Coxiella burnetii IgM phase II for the diagnosis of acute Q fever. Eur J Clin Microbiol Infect Dis 2012; 31 : 1267-70.  Back to cited text no. 20
    
21.
Hackert VH, van der Hoek W, Dukers-Muijrers N, de Bruin A, Al Dahouk S, Neubauer H, et al. Q fever: Single-point source outbreak with high attack rates and massive numbers of undetected infections across an entire region. Clin Infect Dis 2012; 55 : 1591-9.  Back to cited text no. 21
    
22.
Schneeberger PM, Hermans MHA, van Hannen EJ, Schellekens JJA, Leenders ACAP, Wever PC. Real-time PCR with serum samples is indispensable for early diagnosis of acute Q fever. J Clin Microbiol 2010; 26 : 1978-82.  Back to cited text no. 22
    
23.
Zhang GQ, Nguyen SV, To H, Ogawa M, Hotta A, Yamaguchi T, et al. Clinical evaluation of a new PCR assay for detection of Coxiella burnetii in human serum samples. J Clin Microbiol 1998; 36 : 77-80.  Back to cited text no. 23
    
24.
Fournier PE, Raoult D. Comparison of PCR and serology assays for early diagnosis of acute Q fever. J Clin Microbiol 2003; 41 : 5094-8.  Back to cited text no. 24
    
25.
Raele DA, Garofolo G, Galante D, Cafiero MA. Molecular detection of Coxiella burnetii using an alternative Loop-mediated isothermal amplification assay (LAMP). Vet Ital 2015; 51 : 73-8.  Back to cited text no. 25
    
26.
Kantsø B, Svendsen CB, Jørgensen CS, Krogfelt KA. Comparison of two commercially available ELISA antibody test kits for detection of human antibodies against Coxiella burnetii. Scand J Infect Dis 2012; 44 : 489-94.  Back to cited text no. 26
    
27.
Medić S, Kaluski DN, Seguljev Z, Obrenović J, Rudan P, Lazarević M, et al. Q fever outbreak in the village of Noćaj, Srem county, Vojvodina Province, Serbia, January to February 2012. Euro Surveill 2012; 17. pii: 20143.  Back to cited text no. 27
    
28.
Szymańska-Czerwińska M, Galińska EM, Niemczuk K, Knap JP. Prevalence of Coxiella burnetii infection in humans occupationally exposed to animals in Poland. Vector Borne Zoonotic Dis 2015; 15 : 261-7.  Back to cited text no. 28
    
29.
Raven CF, Hautvast JL, Herremans T, Leenders AC, Schneeberger PM. Solitary IgM phase II response has a limited predictive value in the diagnosis of acute Q fever. Epidemiol Infect 2012; 140 : 1950-4.  Back to cited text no. 29
    
30.
Anderson A, Bijlmer H, Fournier P-E, Graves S, Hartzell J, Kersh GJ, et al. Diagnosis and management of Q fever - United States, 2013: Recommendations from CDC and the Fever Working Group. MMWR Recomm Rep 2013; 62 (RR-03) : 1-30.  Back to cited text no. 30
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

Top
 
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

 
  In this article
    Abstract
    Material & M...
   Results
   Discussion
   Acknowledgment
    References
    Article Tables

 Article Access Statistics
    Viewed430    
    Printed5    
    Emailed0    
    PDF Downloaded141    
    Comments [Add]    

Recommend this journal