Fever of unknown origin (FUO). II. Diagnostic procedures in a prospective multicenter study of 167 patients. The Netherlands FUO Study Group

Fever of unknown origin in a Mediterranean survey from a division of internal medicine: report of 91 cases during a 12-year-period (1991-2002)

Despite the availability of all advanced diagnostic tools, fever of unknown origin (FUO) remains a diagnostic challenge for physicians. The objective was to define, through a retrospective study, the categories of the diseases of Sicilian patients admitted at the Department of Clinical Medicine and Emerging Diseases, University of Palermo, Italy, for classical FUO. Using the registration system for patients admitted from 1991 to 2002, 508 charts of patients admitted because of fever were reviewed. Of these, only 91 patients fulfilled the criteria for classical FUO. The origin of FUO was diagnosed in 62 (68.1%) patients. Infection was the most common cause of FUO with 29 cases (31.8% of total of FUO), neoplasms accounted for 13 cases (14.2%), collagen vascular disease for 11 cases (12.0%), and miscellaneous for 9 cases (9.8%). Undiagnosed FUO were 29 (31.8%) and, of them, 22 cases were followed-up for 2 years. A definite diagnosis could be established only in 8 cases, 13 subjects completely recovered and 4 of them died. In the 73.4% of cases, the FUO have been the result of misleading factors in the diagnostic approaches as made by the physician. The results of our study are similar to those already reported by other authors in other populations, with infections as first, neoplasm as second, and collagen vascular diseases as third most important causes of FUO. In our study the prognosis for undiagnosed FUO cases was good, but a definite diagnosis could be established only in few cases. Therefore, further multicentric, prospective studies of good design are required.

Fever of Unknown Origin: Analysis of 71 Consecutive Cases

BACKGROUND

Fever of unknown origin (FUO) is still an important problem in clinical practice. Evaluation of patient characteristics may clarify the utility of diagnostic tests and etiologies of FUO.

METHODS

Fever of unknown origin in 71 patients was investigated at Ankara Numune Education and Research Hospital in Turkey between February 2001 and December 2004.

RESULTS

Mean hospital stay and fever duration was 20.5 days and 44 days, respectively. Etiologies of FUO were as follows: infections 32 (45.1%), collagen vascular disease 19 (26.8%), neoplasm 10 (14.1%), and miscellaneous diseases 4 (5.6%). Diagnosis remained obscure in 6 patients (8.5 %). Tuberculosis was found to be 40% of the infectious causes of FUO. Mean hospital stay and fever duration were prolonged in infectious cases. Female predominance was observed in collagen vascular diseases (P = 0.047). Splenomegaly and lymphadenopathy were common in the neoplasm group (P = 0.017, P = 0.017, respectively). Erythrocyte sedimentation rate, aspartate aminotransferase, alanine aminotransferase and lactate hydrogenase levels were elevated in patients with collagen vascular diseases. Nine (12.7%) patients died during the follow-up period.

CONCLUSIONS

Hospital stay and fever duration were prolonged in the infectious group of FUO patients. Infectious diseases, particularly tuberculosis, were the most important cause of FUO in our series. Tuberculosis should be kept in mind as an important etiology of FUO countries where tuberculosis is endemic.

Fiebre de origen desconocido clásica: cambios en dos series asíncronas en un hospital universitario

We compare two clinical series of patients with fever of unknown origin (FUO) during two different periods of time (1982-1989 and 1997-2004) in the department of Internal Medicine at La Paz University Hospital, Madrid. We have analysed the changes in aetiology and diagnostic methods in these separated periods. We describe a decrease in the incidence of this clinical entity which we think to be due to the improvement of the diagnostic methods. This provides an earlier diagnosis and so patients do not reach criteria for classical FUO. Due to these improvements we have also assessed a change in the final diagnoses and the means used to reach them which, in general, have been less interventionist.

A prospective multicenter study on fever of unknown origin: the yield of a structured diagnostic protocol

We conducted a prospective study to update our knowledge of fever of unknown origin (FUO) and to explore the utility of a structured diagnostic protocol. From December 2003 to July 2005, 73 patients with FUO were recruited from 1 university hospital (n = 40) and 5 community hospitals (n = 33) in the same region in The Netherlands. FUO was defined as a febrile illness of >3 weeks' duration, a temperature of >38.3 degrees C on several occasions, without a diagnosis after standardized history-taking, physical examination, and certain obligatory investigations. Immunocompromised patients were excluded. A structured diagnostic protocol was used. Patients from the university hospital were characterized by more secondary referrals and a higher percentage of periodic fever than those referred to community hospitals. Infection was the cause in 16%, a neoplasm in 7%, noninfectious inflammatory diseases in 22%, miscellaneous causes in 4%, and in 51%, the cause of fever was not found (no differences between university and community hospitals). There were no differences regarding the number and type of investigations between university and community hospitals. Significant predictors for reaching a diagnosis included continuous fever; fever present for <180 days; elevated erythrocyte sedimentation rate, C-reactive protein, or lactate dehydrogenase; leukopenia; thrombocytosis; abnormal chest computed tomography (CT); and abnormal F-fluorodeoxyglucose positron emission tomography (FDG-PET). For future FUO studies, inclusion of outpatients and the use of a set of obligated investigations instead of a time-related criterion are recommended. Except for tests from the obligatory part of our protocol and cryoglobulins in an early stage, followed by FDG-PET, and in a later stage by abdominal and chest CT, temporal artery biopsy in patients aged 55 years or older, and possibly bone marrow biopsy, other tests should not be used as screening investigations.

Fever of unknown origin in adults: evaluation of 144 cases in a non-university hospital

The spectrum of diseases found in series of fever of unknown origin shows variation in relation to selection bias; particularly, selection of the most difficult cases in tertiary reference university centres. We present a series of 144 patients presenting to a non-university hospital between 1999 and 2005 (secondary level of the health care system) with a community-acquired fever of unknown origin. In 37 cases (25.7%), the reason for fever could not be explained. Among the 107 patients with a final diagnosis (74.3%), non-infectious inflammatory disorders represented the most prevalent category (35.5%), surpassing infections (30.8%), miscellaneous causes (20.6%) and malignancies (13.5%). 13 entities accounted for over 68% of diagnoses (sinusitis and occult dental infections, Q fever, Epstein-Barr virus and cytomegalovirus infections, lymphoma, colo-rectal adenocarcinoma, adult-onset Still disease, systemic lupus erythematosus, giant cell arteritis and/or polymyalgia rheumatica, rheumatoid arthritis, polyarteritis nodosa, factitious fever and habitual hyperthermia). As demonstrated in other studies, non-infectious inflammatory diseases emerge as the most prevalent diagnostic category. Giant cell arteritis and polymyalgia rheumatica were particularly frequent in the elderly. Epstein-Barr virus and cytomegalovirus infections and habitual hyperthermia were particularly frequent in the youngest patients. There were no major differences in repartition of diagnostic categories between this series and historical university series.

Fever of unknown origin, infection of subcutaneous devices, brain abscesses and endocarditis

The term 'fever of unknown origin' includes a wide range of conditions that often remain undiagnosed. The possibility of an infection must be promptly diagnosed in order to begin appropriate therapy. Imaging with radiopharmaceuticals, computed tomography, magnetic resonance imaging and ultrasound are the most commonly applied techniques, usually performed in addition to blood tests, biopsies or tissue cultures when required. The lack of comparative studies investigating the accuracy of each radiopharmaceutical for the study of fever of unknown origin was the incentive to perform a meta-analysis of peer articles published between 1981 and 2004 (33 papers) describing the use of nuclear medicine imaging for this purpose. Furthermore, infection of subcutaneous devices, brain abscesses and endocarditis must be considered amongst the causes of fevers of unknown origin. Reviews of 23, 10 and 10 papers, respectively (from 1976 to 2005), were performed on these specific topics. The results may be a useful guide for the choice of the optimal radiopharmaceutical(s) and diagnostic strategy to be applied in each clinical condition and for different aims.

Fever of unknown origin: a systematic review of the literature for 1995???2004

BACKGROUND

Fever of unknown origin (FUO) identifies a pattern of fever with temperature higher than 38.3 degrees C on several occasions over more than 3 weeks, in which the diagnosis remains uncertain after an initial diagnostic work-up. The identification of the cause of FUO is a challenge in clinical practice despite recent advances in diagnostic techniques. There are more than 200 reported causes of FUO and they can be classified in four diagnostic categories: infections, neoplasms, non-infectious inflammatory diseases and miscellaneous.

METHODS

We performed a systematic research of the literature on classical FUO to retrieve the review articles and case series published from 1995 to 2004, including articles from developing countries. The case series were reviewed to identify the tests commonly used both to qualify a fever as FUO and to determine the cause of the FUO, and to design an updated flow chart for the diagnosis of classical FUO.

RESULTS AND CONCLUSIONS

No standardized diagnostic strategy could be determined. The diagnostic process should be guided by the potential diagnostic clues (PDCs) emerging from the history, physical examination and baseline tests. A standardized flow chart can be applied only in absence of PDCs or when the PDCs are contradictory.Nuclear medicine techniques are a valuable aid in the search for the origin of FUO due to bacterial infections or in the absence of PDCs.

[Empirical treatment of granulomatous hepatitis of unknown origin: practice investigation in the French National Society of Internal Medicine]

PURPOSES

Ten to fifteen percent of granulomatous hepatitis are idiopathic. If symptoms like prolonged fever are present, empirical treatment is discussed. The goal of this study is to describe the empirical treatment proposed in this situation by French specialists of internal medicine.

METHODS

We conducted a practice investigation among the French national society of internal medicine (SNFMI), using an anonymous questionnaire that related a case of idiopathic granulomatous hepatitis. This questionnaire was proposed to all French internists present at the SNFMI congress in June and December 2004. French specialists of internal medicine had to answer if they would prescribe an empirical treatment and if so, to specify this treatment.

RESULTS

Thirty-six French specialists of internal medicine answered to the questionnaire. In the proposed situation, 89% of them initiate an empirical treatment. In 18/36 cases (50%), a first-line anti-tuberculosis empirical treatment is proposed (quadritherapy in 11 cases). In 7 cases (19%), an empirical treatment with prednisone, 0.4 mg/kg/d (N=1) and 1 mg/kg/d (N=6), would be prescribed. Seven internists (19%) would prescribe an empirical treatment with cyclins at the dose of 100 to 400 mg/d. Median duration of the empirical treatment would be 28 days (range: 8-252d). The evaluation parameters mentionned are: fever (69%), weight (59%), seric level of C-reactive protein (59%), and liver biology (53%). In case of failure of first-line empirical treatments, 69% of all questionned internists prescribe a second-line treatments: prednisone at the dose of 0.4 to 2 mg/kg/d (72%), anti-tuberculosis treatments (16%), cyclins 200 mg/d (12%), with a median duration of 28 days. Seven internists (19%) propose to combine two empirical treatments.

DISCUSSION

Faced with a problem of idiopathic granulomatous hepatitis, French internists questionned propose four therapeutics options: no treatment, anti-tuberculosis treatment, cyclins or steroids treatment. First-line anti-tuberculosis treatment is a coherent proposition regarding to the high prevalence of tuberculosis. There are only few data available concerning empirical treatment with steroids or cyclins. Specific proposition of such empirical treatments should be defined.

CONCLUSIONS

The management of idiopathic granulomatous hepatitis is difficult. Our study shows that therapeutics practices of French internists are heterogenous. The main proposition consists in a first-line anti-tuberculosis empirical treatment, that has to be evaluated after four weeks, and switched with steroids (prednisone, 1 mg/Kg/d) in case of failure. This study is not an expert proposition but contributes to suggest clinical practice guidelines for a rare, complex, heterogenous, and typically internist situation.

Fever of unknown origin: what is remarkable in the elderly in a developing country?

OBJECTIVES

To investigate fever of unknown origin (FUO) in 97 patients and compare geriatric and adult population.

METHODS

We investigated 97 (22 elderly) patients with FUO using the criteria of Petersdorf and Beeson [Medicine 40 (1961) 1] hospitalized between January 1990 and May 2005 at Hacettepe University Hospital.

RESULTS

Infectious diseases were the most common cause in the adult (33.3%) and the elderly (45.5%) patients both. Neoplasms were seen in 18.7; 4.5% and collagen vascular diseases were diagnosed in 9.3; 4.5% of the adults and the elderly respectively. Tuberculosis accounted for 60% of all the infectious causes and empirical anti-tuberculous treatment served as a diagnostic method in 43% of the cases with tuberculosis. Lymphadenopathy was more common among the adults with FUO. A diagnosis could be reached in all the elderly patients with a very high erythrocyte sedimentation rate (ESR>100mm/h). At the end of the hospitalization, 14.7% (11/75) of the adult patients and 13.6% (3/22) of the elderly patients died.

CONCLUSION

Geriatric patients with FUO usually have characteristics similar to the adult patients with respect to the hospitalization time, diagnosis, and inpatient mortality. Lymphoid organ hyperplasia might be expected less frequently and very high ESR might be a more reliable indicator of systemic disease in the elderly. Empirical anti-tuberculous treatment plays an important diagnostic role in the developing countries with a higher prevalence of tuberculosis.

[Renal angiomyolipoma and fever: assessment with isotopic renogram and 67Ga scintigraphy]

A 26 year-old woman with tuberous sclerosis who came to the Emergency Department with high fever, bilious vomit, right hemiabdomen pain and syncope during 2 weeks. Laboratory analyses show hemoglobin 6.7 g/dl, creatinine 1.5 mg/dl and leukocytes 30,000. Abdominal CT is performed because of suspicion of active bleeding in right hemiabdomen, following rupture of right angiomyolipoma, treated by selective arterial embolization. She was referred to the Nuclear Medicine Department to perform a 67Gallium scintigraphy for the detection of infection, and static and dynamic renal scintigraphy for evaluation of the renal morphology and function.

Distinguishing among prolonged, recurrent, and periodic fever syndromes: approach of a pediatric infectious diseases subspecialist

Most children with prolonged, recurrent, or periodic fever are healthy and have self-limited, common illnesses, and the primary care practitioner usually can reassure families and continue to reassess the patient as circumstances dictate. For a child with true fever of unknown origin, a pediatric infectious diseases subspecialist should be consulted. This article discusses three objectives for the clinician: (1) to categorize patterns of fever illnesses and prioritize differential diagnoses; (2) to diagnose and manage the most frequently encountered prolonged fever syndrome, deconditioning; and (3) to expand knowledge and approach to diagnosing periodic fever syndromes. The approach described in this article represents the honed, 30-year experience of a pediatric infectious diseases subspecialist.

Standardised work-up programme for fever of unknown origin and contribution of magnetic resonance imaging for the diagnosis of hidden systemic vasculitis

BACKGROUND

Fever of unknown origin (FUO) is a diagnostic challenge. Rheumatologists are often in charge of patients with FUO because the vasculitides, especially, are potential and common causes of FUO.

OBJECTIVE

To evaluate the value of a standardised investigation to identify the cause of FUO.

METHODS

A standardised work-up programme for patients with FUO was started at the beginning of September 1999. The rate of identified causes of FUO was compared between all patients with FUO admitted to a tertiary care centre of rheumatology between January 1996 and August 1999 (control group) and September 1999 and January 2003 (work-up group). In January 2002 magnetic resonance imaging (MRI) was added to the investigation.

RESULTS

67 patients with FUO were identified--32 before and 35 after institution of the work-up programme. Before implementation 25% of all patients with FUO remained undiagnosed, after implementation 37%. After institution of the investigation the percentage of patients with vasculitides increased significantly from 6% (n = 2) to 26% (n = 9, p = 0.047, Fisher's exact test). This increase could be attributed to the addition of MRI in 2002. When all patients with FUO before 2002 (n = 55) and thereafter (n = 12) were compared the prevalence of systemic vasculitis increased from 11% (n = 6) to 42% (n = 5, p = 0.021).

CONCLUSION

Implementation of a standardised work-up programme for FUO did not improve the overall rate of diagnosis. Addition of MRI significantly increased the diagnosis of systemic vasculitis as the underlying cause of FUO. MRI should be included in the investigation of patients with FUO when vasculitis is suspected.

Rentabilidad de la tomografía axial computarizada en el diagnóstico de la fiebre de origen desconocido clásica

Diagnostic strategy in fever of unknown origin has been changing in recent decades. The objective of this study is to define the role of thoracoabdominal computerized axial tomography in the first diagnostic stage. A sample of 24 patients with classical fever of unknown origin from our hospital Internal Medicine department was selected between January 1995 and December 2002. Cost-effectiveness of diagnostic thoracoabdominal computerized axial tomography compared to that of abdominal echography was analyzed; the information obtained with both diagnostic techniques for the final diagnosis was also evaluated. Computerized axial tomography contributed data suggestive of the diagnosis in 10 of 24 patients (41.7%); abdominal echography only gave orienting information to the diagnosis in 2 cases (8%). In 9 (90%) of the 10 patients with computerized axial tomography specific alterations, a conclusive definitive diagnosis (with analysis of biological sample) was possible. Accordingly, the use of this technique is justified at the beginning of the study of the classical fever unknown origin in order to orient the clinician to resort to other more directed and specific diagnostic techniques and with higher diagnostic cost-effectiveness.

Fever of unknown origin-predictors of outcome. A prospective multicenter study on 164 patients

BACKGROUND: To date, the studies that have been done on fever of unknown origin have mostly been descriptive. Therefore, we know the etiogical spectrum and how it has changed since 1966 for many regions of the world. However, we do not know if there are clinical or laboratory predictors of severe outcome. Being able to estimate the severity of the disease early on would allow one to determine how intensive the diagnostic work-up should be. METHODS: A multicenter cohort study was carried out on 164 consecutive patients who met the classic, modified criteria of fever of unknown origin. The study lasted 2 years (1997-1998) and included a follow-up period of another 2 years. The main outcome measured was the final diagnosis established at the end of follow-up. RESULTS: When the white cell count was abnormal, the relative risk for a serious disease was 1.49 (CI: 1.15-1.94; p=0.004), when anemia was present, the relative risk was 1.55 (CI: 1.21-1.98; p=0.003), and for high alanine aminotransferase (ALAT), bilirubin, or lactate dehydrogenase (LDH), the relative risks were 1.57 (CI: 1.21-2.02; p=0.010), 1.57 (CI: 1.18-2.08; p=0.007), and 3.43 (CI: 1.81-6.48; p=0.0002), respectively. In multivariate analysis, the odds ratios for serious diseases were 2.7 (CI: 1.17-6.4; p=0.02) for abnormal white cell count, 2.8 (CI: 1.14-7.16; p=0.02) for anemia, 4.3 (CI: 1.6-11.5; p=0.003) for high serum bilirubin, and 5.3 (1.5-18.6; p=0.009) for high serum ALAT. CONCLUSIONS: In patients having a fever of unknown origin, anemia, abnormal white cell count, and high ALAT and bilirubin are independent predictors of severe outcome.

Unexplained fever in the ED: analysis of 139 patients

This study examined consecutive patients with unexplained fever (UF) presenting to the ED to define their characteristics and to compare distinctive parameters between admitted and discharged patients. During a 3-month period, all adult patients presenting to the ED with UF were prospectively followed for 1 month. Of 139 patients with UF, 58 patients (42%) were admitted to the hospital, whereas 81 patients (58%) were discharged. Whereas most of the discharged patients had self-limited febrile disease and eventually recovered, the admitted patients had more unresolved fever, serious infections, or systemic diseases and a 5% mortality rate. The admitted patients were older, had more comorbidity, higher leukocyte count, and anemia, but not a higher degree of fever. Older age, comorbidity, leukocytosis, and anemia, but not higher degree of fever, should direct the decision toward admission of a patient with UF.

Fever of unknown origin in adults: 40 years on

A revision of the criteria of fever of unknown origin (FUO), established in 1961, is desirable because of important evolutions in medical practice and the emergence of new patient populations. The development of rapid laboratory tests and powerful diagnostic tools, such as ultrasonography, computed tomography and magnetic resonance imaging often makes hospitalization unnecessary and new categories of patients such as those with HIV infection, neutropenia, immunosuppression and nosocomial illness require an approach different from classical FUO. The more then 200 reported causes of FUO can be classified into four diagnostic categories; infections, tumours, noninfectious inflammatory diseases (NIID) and miscellaneous. A uniform classification system is highly wanted to allow comparison between different series. The reports of the 1990s show slight changes in the distribution of causes, namely less infections, less tumours, more NIID and more undiagnosed cases. A uniform diagnostic strategy cannot be determined. The initial investigation should be directed by potentially diagnostic clues revealed by extensive history, meticulous physical examination and a standard set of laboratory tests. 18Fluoro-deoxy-glucose-positron-emitted-tomography is a new valuable total body scintigraphy in the search for the site of origin of the fever. In view of the rather good long-term prognosis, a wait-and-see strategy may be more appropriate than a systematic staged approach. Elderly patients and patients with episodic fever represent two specific groups of classical FUO that require a distinct approach. HIV-associated, nosocomial and neutropenic FUO should be considered as separate clinical entities.

[Fever of intermediate duration]

Fever of intermediate duration (FID) is defined as non-localized fever occurring in the community, lasting from one to four weeks, and having no diagnostic orientation after basic clinical, analytical and radiological evaluations are completed. These may include careful recording of clinical history, physical examination, hemogram, plasma creatinine determination, urinalysis, and chest radiography. The etiology of FID is still not completely defined. In our country, 70% of cases are caused by systemic infectious diseases (rickettsiosis, brucellosis, and mononucleosis syndrome) and 7.7% by localized infections; vasculitis and neoplasms account for less than 2%. In most cases FID can be attended on an outpatient basis, with the guarantee of the easy accessibility. In cases without social support or when there is digestive intolerance or criteria of severe disease, hospital care is required. For the diagnostic approach, it is useful to establish basic rules and to organize the study in several stages, taking into account the most frequent etiologies. The first visit would include elaboration of the clinical history, a hemogram, biochemistry analyses, blood cultures, urine culture, serological studies for the most frequent etiologies, a chest radiograph, and other examinations, as indicated by the clinical history data. The care provided and subsequent diagnostic studies performed will depend on the patient's progression and findings from additional studies. Further works conducted in various geographic settings are necessary to define the complete etiological spectrum of FID.

[Development and long-term prognosis of unexplained persistent inflammatory biologic syndromes]

PURPOSE

Unexplained inflammatory syndrome is a frequent and worrying condition in Internal Medicine. However, the long-term clinical outcome of these patients cannot be inferred from the literature. The aim of this study is to describe the long-term follow-up and the prognosis of a group of patients hospitalised for an inflammatory syndrome and discharged without causal diagnosis.

METHODS

This retrospective study was carried out on 46 patients, 15 men and 31 women, aged 21 to 90 years, hospitalised between 1992 and 1999. Data concerning the hospital stay were obtained from the patients' medical record. Follow-up was performed by consulting the treating physician.

RESULTS

The prognosis of these patients is fairly good. In one third of the cases, the inflammatory syndrome resolved spontaneously (n = 13). In the second third, a definite diagnosis was established after discharge (n = 14) and consisted mainly of chronic inflammatory diseases (n = 9), cured with a specific treatment. In the remaining third (n = 12), the inflammatory syndrome persisted, in clinically asymptomatic patients.

CONCLUSION

These results suggest that the persistence of an inflammatory syndrome is not a poor prognostic factor. Thus we propose for patients discharged with an undiagnosed persistent inflammatory syndrome despite thorough investigations, a simple clinical and biological follow-up instead of repeated etiological investigations.

Tuberculosis as a cause of recurrent fever of unknown origin

Recurrent fever constitutes a diagnostic challenge for clinicians, due mainly to the intermittent nature of the fever that results in incomplete investigations. We describe three patients with recurrent fever thought to be due to tuberculosis, and review the 14 previously reported cases who fulfil the criteria of recurrent fever for at least 1 month's duration. The median duration of symptoms before diagnosis was 5 months, and the duration of the febrile bouts ranged from a few hours to 1 week. The most common complaints were constitutional symptoms and abdominal pain, and most patients had significant underlying conditions. The mortality rate was 31%, and was limited to the earlier cases. Routine laboratory studies are not very helpful for the diagnosis of this condition, and chest radiographs showed some alteration in half the cases at the time of diagnosis, although in some cases represented old, healed lesions. PPD testing was positive in most cases, particularly in those without underlying conditions. Empirical antituberculous therapy should be considered in cases of recurrent fever, especially in areas of high prevalence or in patients with predisposing conditions.

Human and animal epidemic of Yersinia enterocolitica O:9, 1989-1997, Auvergne, France

Yersinia enterocolitica O:9 infections were reported in Auvergne in 1988 to 1989, while brucellosis due to Brucella abortus was almost eliminated. The serologic cross-reactions between the two bacteria complicated the diagnosis of brucellosis cases. In 1996, human cases of Yersinia enterocolitica O:9 infection were detected, with a peak incidence of 12 cases. Veterinary surveillance could have predicted the emergence of this disease in humans.

Fever of unknown origin (FUO). I A. prospective multicenter study of 167 patients with FUO, using fixed epidemiologic entry criteria. The Netherlands FUO Study Group

Internal medicine wards in all 8 university hospitals in the Netherlands participated in this prospective study of fever of unknown origin (FUO) from January 1992 until January 1994 in order to update information on the spectrum of diseases causing FUO. We used fixed epidemiologic entry criteria to achieve completeness of enrollment and to avoid unintended selection bias. After entry, immunocompetent patients were included using criteria for FUO according to Petersdorf and Beeson (30). A standardized diagnostic protocol was used, and potentially diagnostic clues (PDCs) and their use in the diagnostic process were prospectively registered. Thus, the criteria of classic FUO have been adjusted to modern times: immunocompromised patients are excluded, and the time-criterion "1 week in hospital without a diagnosis" has been replaced by a quality-criterion stating that certain investigations must be performed as a minimum, and PDCs must be followed adequately for at least 1 week, without a diagnosis being reached. A total of 167 immunocompetent patients with FUO were thus retrieved, of whom 43 (25.7%) had infections, 21 (12.6%) had neoplasms, and 40 (24.0%) had noninfectious inflammatory diseases. No diagnosis was made in 50 patients (29.9%), 37 of whom recovered spontaneously. This study confirms the changing spectrum of diseases causing FUO. Indeed, as shown by another recent study, the group of patients with FUO in whom no diagnosis can be made is expanding, and mostly it concerns self-limiting or benign fevers. Others have suggested that this trend is not really occurring (29). We did not place patients with diseases of unknown origin in the "nondiagnosis" group, and indeed made presumptive diagnoses when necessary. Nevertheless, this category of undiagnosed fevers is increasing. We believe that the higher percentage of undiagnosed cases can be attributed to the greater use of advanced diagnostic techniques attendant on an increased number of self-limited illnesses in patients meeting criteria for FUO. Because of ongoing development in diagnostic techniques and the prospective influence on the spectrum of diseases causing FUO, studies should be performed regularly to update information on this subject. Because the number of outpatient evaluations for FUO is expected to increase, patients seen on an outpatient basis should be included in future studies. To avoid unwanted selection bias, fixed epidemiologic entry criteria should be used to ensure completeness of enrollment. To shorten the period of collecting data, multicentric studies can be done using standardized diagnostic protocols. In patients with recurrent fever or fever lasting longer than 6 months, the chance of reaching a diagnosis is significantly lower, and especially in this group one should exercise the greatest caution to avoid abundant and extensive diagnostic procedures. The diagnostic process in patients with FUO remains an intriguing problem in medicine. Recent microbiologic techniques may be useful as an approach to the relatively large proportion of patients in whom we now fail to make a diagnosis.