Genitourinary tuberculosis: a review of 174 cases

Genitourinary Tuberculosis: A Comprehensive Review of a Neglected Manifestation in Low-Endemic Countries

Genitourinary tuberculosis (GUTB) represents a disease often underestimated by urological specialists, particularly in settings such as the European one, where the pathology is less frequent. Similar to other uncommon diseases at these latitudes, GUTB is a neglected clinical problem. In this light, the aim of this review is to give a comprehensive overview of GUTB in order to provide a useful tool for urologists who seldomly manage this disease. A non-systematic review of genitourinary tuberculosis was performed on relevant articles published from January 1990 to July 2021 using PubMed, Scopus, and the Cochrane Central Register of Controlled Trials. GUTB represents up to a quarter of extrapulmonary tuberculosis (EPTB) cases. Diagnostic, therapeutic and surgical work-up have been deeply reviewed and summarized. The mass migration of refugees to Europe as well as the ease of international travel is gradually leading to an upsurge in urological diseases such as GUTB, which were previously only rarely encountered in some European countries. The poor TB knowledge of European urologists should be improved through medical education courses, webinars or telematic means.

The impact of orthotopic reconstruction on female sexuality and quality of life after radical cystectomy for non-malignant bladder conditions

OBJECTIVE

To review the literature on the impact on female quality of life and sexual function of orthotopic reconstruction after radical cystectomy for non-malignant bladder conditions. Radical cystectomy is commonly required to treat malignant conditions but may also be considered for the treatment of non-malignant diseases. These heterogeneous group of disorders includes interstitial cystitis, painful bladder syndrome, neurogenic bladder, haemorrhagic/ radiation cystitis, endometriosis and refractory genitourinary fistula. Treatment begins with non-invasive medical therapies but, in non-responder cases, a surgical solution should be considered. Such invasive techniques include urinary diversion and reconstructive procedures that have an impact on healthrelated quality of life, physical, social, and mental status.

MATERIALS AND METHODS

This narrative review research was done using the PubMed database up until 2020, July. All papers referring to cystectomy for benign indication were considered.

RESULTS

In comparison to other reconstructive options, orthotopic neobladder allows the restoration of a normal self-image and consequently it is the most suitable procedure when a surgical reconstruction is necessary for non-malignant conditions. However, women can face many disorders that impact on everyday life, such as voiding dysfunction or sexual activity problems.

CONCLUSIONS

Scant data is available about quality of life, sexual life and self-perception in women treated by cystectomy for benign conditions and most literature is dedicated to those indicators in cancer patients. More research is needed to understand the tolerability and the quality of life results of the female population affected by benign conditions undergoing this kind of surgical approach.

Update on urogenital tuberculosis in Southern Tunisia: a review of a 26-year period

Introduction

Tuberculosis affects commonly the lungs, but any other organs can be affected as well. Urogenital tuberculosis is usually misdiagnosed. In this perspective, we aimed to give an update on the epidemiological, clinical and evolutionary features of urogenital tuberculosis in Southern Tunisia.

Methods

We conducted a retrospective study including all patients with extrapulmonary tuberculosis notified during the period from 1992 to 2017 in Southern Tunisia. We specified the particularities of urogenital tuberculosis cases, and we compared them with other extrapulmonary tuberculosis cases.

Results

Overall, we analyzed 240 cases with urogenital tuberculosis, among 1702 patients with extrapulmonary tuberculosis (14.1%). There were 121 women (50.4%). The mean age was 49±17 years. Multifocal tuberculosis was noted in 29 cases (12.1%). There were 169 cases with urinary tract tuberculosis (70.4%). Chronological trends analysis showed that the median age at diagnosis increased significantly (Rho=0.41; p=0.039) and the number of urogenital tuberculosis declined during the study period, without a statistical significance (Rho = -0.07; p=0.721). Compared to other extrapulmonary tuberculosis sites, patients aged 60 years and above (OR=2.7; p<0.001) and coming from rural areas (OR=1.4; p=0.021) were more frequently diagnosed with urogenital tuberculosis. Treatment duration was significantly longer in patients with urogenital tuberculosis (10.13±3.79 vs 9.20±3.77 months; p<0.001). As for the disease evolution, relapse was significantly more frequent in patients with urogenital tuberculosis (OR=4.1; p=0.045).

Conclusions

Although decreasing trends over time were noted, the prognosis of urogenital tuberculosis was more severe compared to other extrapulmonary tuberculosis sites.

Extensive Primary Male Genital Tuberculosis

Genital tuberculosis (GTB) is uncommon, and the most common genital sites of tuberculous infection are epididymis and prostate; isolated testicular TB is extremely rare, comprising only 3% of GTB. The usual modes of genital involvement include descending infection from the kidneys, intracanalicular or direct extension from neighboring foci in the genital tract, and hematogenous dissemination. Ultrasonography (USG) and USG-guided fine-needle aspiration cytology of testicular swelling may confirm the diagnosis of GTB. Anti-TB chemotherapy is the mainstay of treatment to ensure the complete resolution of the lesion. Infertility in GTB is a result of obstruction at the terminal portion of the ejaculatory duct, resulting in dilatation of the proximal ductal system including the vas deferens preventing seminal vesicle secretions from reaching the ejaculate. Seminal vesicle secretions make up the bulk of the ejaculate, contain fructose, and alkalinize the ejaculate, and with obstruction, patients present with azoospermia or aspermia. Here, we present a rare case of extensive primary GTB in a 36-year-old male.

Urogenital tuberculosis - epidemiology, pathogenesis and clinical features

Tuberculosis (TB) is the most common cause of death from infectious disease worldwide. A substantial proportion of patients presenting with extrapulmonary TB have urogenital TB (UG-TB), which can easily be overlooked owing to non-specific symptoms, chronic and cryptic protean clinical manifestations, and lack of clinician awareness of the possibility of TB. Delay in diagnosis results in disease progression, irreversible tissue and organ damage and chronic renal failure. UG-TB can manifest with acute or chronic inflammation of the urinary or genital tract, abdominal pain, abdominal mass, obstructive uropathy, infertility, menstrual irregularities and abnormal renal function tests. Advanced UG-TB can cause renal scarring, distortion of renal calyces and pelvic, ureteric strictures, stenosis, urinary outflow tract obstruction, hydroureter, hydronephrosis, renal failure and reduced bladder capacity. The specific diagnosis of UG-TB is achieved by culturing Mycobacterium tuberculosis from an appropriate clinical sample or by DNA identification. Imaging can aid in localizing site, extent and effect of the disease, obtaining tissue samples for diagnosis, planning medical or surgical management, and monitoring response to treatment. Drug-sensitive TB requires 6-9 months of WHO-recommended standard treatment regimens. Drug-resistant TB requires 12-24 months of therapy with toxic drugs with close monitoring. Surgical intervention as an adjunct to medical drug treatment is required in certain circumstances. Current challenges in UG-TB management include making an early diagnosis, raising clinical awareness, developing rapid and sensitive TB diagnostics tests, and improving treatment outcomes.

Genitourinary tuberculosis in Taiwan: A 15-year experience at a teaching hospital

BACKGROUND

Genitourinary tuberculosis (GUTB) is rare but fatal if not diagnosed early. The purpose of this study was to investigate the outcomes of GUTB in Taiwan.

METHODS

We retrospectively reviewed medical records of 57 patients who were diagnosed as GUTB from January 2002 to December 2016, over a 15-year period. Demographic data and clinical manifestations were recorded for analysis.

RESULTS

There were 37 males and 20 females with a median age of 71 years. Kidney (24.6%) was the most involved organ. Fever (56.1%) was the major presentation. Sixteen (28.1%) patients presented unfavorable outcome. Compared with the favorable outcome group, the unfavorable outcome group had more malignancy (p = 0.013), fever (p = 0.020), anemia (p = 0007), thrombocytopenia (p = 0.003), and hypoalbuminemia (p = 0.015). In a multivariate analysis, fever (odds ratio: 42.716, 95% confidence interval: 1.032-1767.569; p = 0.048) was identified as prognostic factors for unfavorable outcome.

CONCLUSION

GUTB is often in advanced stages with a high mortality in Taiwan. Establishing a diagnosis is difficult and requires thorough investigation. Fever is associated with unfavorable outcome.

Medical treatment for urogenital tuberculosis (UGTB)

Urogenital tuberculosis (UGTB) should in general be treated as pulmonary TB with a four-drug regimen of Isoniazid, Rifampicin, Ethambutol and Pyrazinamide for a total of 6 months, Ethambutol and Pyrazinamide only the first two months. Some patients may need longer treatment (cavitary disease, kidney abscess/malfunction, HIV co-infection). Treatment of multi-drug resistant tuberculosis (MDR-TB) requires use of long-term intravenous treatment with aminoglycosides and other drugs with considerable toxicity for 18–24 months. Complications such as urinary tract obstruction may occur and should be treated with corticosteroids or surgery.

Tuberculosis epididymitis complicated by a cutaneous fistula

A 63-year-old man developed scrotal swelling that became bilateral over 2 months. His symptoms persisted after treatment for epididymitis, and he developed a scrotal fistula with drainage. Mycobacterium tuberculosis grew from the urine and fistula. His symptoms resolved and fistula closed with medical therapy. His case highlights the importance of early recognition, diagnosis and treatment of this form of extrapulmonary tuberculosis.

Urogenital Tuberculosis

Urogenital tuberculosis is the second most frequent form of extrapulmonary tuberculosis. Starting with a pulmonary focus, 2 to 20% of patients develop urogenital tuberculosis through hematogenous spread to the kidneys, prostate, and epididymis; through the descending collecting system to the ureters, bladder, and urethra; and through the ejaculatory ducts to the genital organs. Urogenital tuberculosis occurs at all age ranges, but it is predominant in males in their fourth and fifth decades. It is a serious, insidious disease, generally developing symptoms only at a late stage, which leads to a diagnostic delay with consequent urogenital organ destruction; there are reports of patients with renal failure as their initial clinical presentation. Although the condition has been long recognized by nephrologists, urologists, and infectious disease specialists, urogenital tuberculosis is still largely unknown. Even when suggestive findings such as hematuria, sterile pyuria, and recurrent urinary infections are present, we rarely remember this diagnostic possibility. Greater knowledge of the features of urogenital tuberculosis then becomes relevant and should emphasize the importance of an early diagnosis.

Genital tuberculosis: current status of diagnosis and management

Genitourinary Tuberculosis (GUTB) is the second most common extra-pulmonary manifestation of tuberculosis (Tb) and an isolated involvement of genital organs is reported in 5–30% of the cases. Genital involvement results from primary reactivation of latent bacilli either in the epididymis or the prostate or by secondary spread from the already infected urinary organs. The epididymis are the commonest involved organs affected primarily by a hematogenous mode of spread. Tb is characterized by extensive destruction and fibrosis, thus an early diagnosis may prevent function and organ loss. The gold standard for diagnosis is the isolation and culture of mycobacterium tuberculosis bacilli and in the cases of suspected GUTB, it is commonly looked for in the urinary samples. All body fluid specimens from possible sites of infection and aspirates from nodules must also be subjected to examination. Radiologic investigations including ultrasonography and contrast imaging may provide supportive evidence. Anti-tubercular chemotherapy is the first line of management for all forms of genital Tb and a 6 months course is the standard of care. Most patients with tubercular epididymo-orchitis respond to antitubercular therapy but may require open or percutaneous drainage. Infertility resulting from the tubercular affliction of the genitalia is multifactorial in origin and may persist even after successful chemotherapy. Multiple organ involvement with obstruction at several sites is characteristic and most of these cases are not amenable to surgical reconstruction. Thus, assisted reproduction is usually required. Post treatment, regular annual follow up is recommended even though, with the current multi drug therapy, the chances of relapse are low.

Urinary tuberculosis: a cohort of 79 adult cases

We aimed to investigate the demographic, clinical, diagnostic, treatment and outcome features of patients with urinary tuberculosis (UTB). Patients with UTB admitted to seven separate centers across Turkey between 1995 and 2013 were retrospectively evaluated. The diagnosis of UTB was made by the presence of any clinical finding plus positivity of one of the following: (1) acid-fast bacilli (AFB) in urine, (2) isolation of Mycobacterium tuberculosis, (3) polymerase chain reaction (PCR) for M. tuberculosis, (4) histopathological evidence for TB. Seventy-nine patients (49.36% male, mean age 50.1 ± 17.4 years) were included. Mean time between onset of symptoms and clinical diagnosis was 9.7 ± 8.9 months. The most common signs and symptoms were hematuria (79.7%), sterile pyuria (67.1%), dysuria (51.9%), weakness (51.9%), fever (43%) and costovertebral tenderness (38%). Cystoscopy was performed in 59 (74.6%), bladder biopsy in 18 (22.8%), kidney biopsy in 1 (1.26%) and nephrectomy in 12 (15.2%) patients. Histopathological verification of UTB was achieved in 12 (63.1%) patients who undergone biopsy and in 100% of those undergone nephrectomy. Mycobacterium tuberculosis was isolated in the urine of 50 (63.3%) cases. Four-drug standard anti-TB treatment was the preferred regimen for 87.3% of the patients. Mean treatment duration was 10.5 ± 2.7 months. Deterioration of renal function occurred in 15 (18.9%) patients two of whom progressed to end-stage renal disease and received hemodialysis. Only one patient died after 74-day medical treatment period. Cases with UTB may present with non-specific clinical features. All diagnostic studies including radiology, cyctoscopy and histopathology are of great importance to exclude UTB and prevent renal failure.

[Investigation and management of genito-urinary tuberculosis]

Genito-urinary tuberculosis is the fourth most common manifestation of the disease, but it is often underestimated by clinicians because of few and non-specific symptoms and insidious disease course. The most common urinary findings are multiple ureteral stenosis. The most common genital involvement is an epididymal nodule for men and a chronic salpingitis for women. The definite diagnosis of genito-urinary tuberculosis is obtained on the basis of culture studies. Due to the paucibacillary nature of the disease, especially of genital location in woman, a probable or presumptive diagnosis is frequently considered with several parameters including radiological imaging (abdominal CT-scan, pelvic ultrasound, pelvic MRI). Endoscopic and surgical procedures are frequently required to obtain specimens for histopathologic and bacteriological studies. Medical treatment is the method of choice, with a combination of four drugs, namely isoniazid, rifampicin, ethambutol and pyrazinamide, followed by a two-drug regimen, for a total of six month duration. Surgery might be indicated in complicated genito-urinary tuberculosis (decreased renal function, infertility, urologic complaints).

Spectrum of urogenital tuberculosis

Urogenital tuberculosis (UGTB) plays an important role because its complications may be fatal, it significantly reduces quality of life, and it is often associated with AIDS. Diagnosis of UGTB is often delayed. We analyzed 131 case histories of UGTB patients from the years 2009-2011. Gender, age, and the clinical form and main features of the disease were taken into account. The most common form was kidney tuberculosis (74.8%). Isolated kidney tuberculosis (KTB) more often occurs in women: 56.8%. Patients of middle and old age more often showed the stage of cavernous KTB; younger patients had smaller forms. Among all cases, an asymptomatic course was seen in 12.2% and, among cases of KTB, in 15.9%. Every third patient complained of flank pain and dysuria (35.2% and 39.8%, respectively); 17% presented with toxicity symptoms, 9.1% with renal colic, and 7.9% with gross hematuria. Mycobacterium tuberculosis (MTB) in urine was found in 31.8% of cases in all levels of isolated KTB. UGTB has no specific symptom; even sterile pyuria occurs only in 25%. The acute onset of tuberculous orchiepididymitis was seen in 35.7% of patients, hemospermia in 7.1%, and dysuria in 35.7%. The most common complaints for prostate tuberculosis were perineal pain (31.6%), dysuria (also 31.6%), and hemospermia (26.3%). MTB in prostate secretion/ejaculate was revealed in 10.5% of this group. All urogenital tract infections should be suspected as UGTB in patients who are living in a region with a high incidence rate, who have had contact with tuberculosis infection, and who have a recurrence of the disease that is resistant to standard therapy.

Be alert to tuberculosis-mediated glomerulonephritis: a retrospective study

Mycobacterium tuberculosis infection causing glomerulonephritis is a rare disorder. This retrospective study analyzed the clinical characteristics of patients diagnosed with tuberculosis-mediated glomerulonephritis (TB-GN) between 2002 and 2009, as well as the diagnostic tools used. These findings were then compared with those of patients with primary glomerulonephritis (P-GN). The records of all patients were reviewed. The diagnosis of TB-GN was based on renal hematuria and/or proteinuria and cure after antituberculosis therapy alone plus urine culture positive for M. tuberculosis, demonstration of typical tubercle granulomas on renal biopsy specimens, or the detection of M. tuberculosis DNA by polymerase chain reaction (PCR) on renal specimens. Forty-six patients with TB-GN and 49 patients with P-GN were included. Compared with patients in the P-GN group, most (76%) patients with TB-GN had a history of TB. Systemic symptoms were much more frequent in patients with TB-GN than local genitourinary symptoms. Serological testing showed a statistical difference between the two groups. Immunoglobulin A nephropathy was found in the majority (72%) of patients with TB-GN. M. tuberculosis DNA detection was positive in 39 (84.8%) patients, a much higher positive rate of diagnosis than that with urine culture for M. tuberculosis. The manifestation of TB-GN is atypical and nonspecific. It warrants a high index of suspicion when patients with renal hematuria and proteinuria fail to respond to standard treatments for P-GN. Clinicians should pay close attention to the medical history and results of special laboratory tests. M. tuberculosis DNA detection on renal biopsy specimens should be considered in order to confirm the diagnosis of TB-GN.

Unilateral testicular tuberculosis: case report

Genitourinary tuberculosis (GT) includes 8-15% of extrapulmonary tuberculosis (TB), which is more frequent in men. Epididymides, seminal vesicles, prostate and testis are the most common sites of GT. Although testicular TB is uncommon, we report 2 patients with unilateral testicular TB. The main treatment of urogenital tuberculosis is anti-tuberculosis pharmacotherapy, sometimes combined with surgery.

Clinical and microbiological characteristics of urine culture-confirmed genitourinary tuberculosis at medical centers in Taiwan from 1995 to 2007

All patients with urine culture-confirmed genitourinary tuberculosis (GUTB) diagnosed between 1995 and 2007 at two medical centers in northern Taiwan were included in this retrospective study. Genotypes of 48 preserved Mycobacterium tuberculosis (MTB) isolates from these patients were determined by spoligotyping and double repetitive element PCR (DRE-PCR) analysis. Among the 64 patients, 38 (59.4%) were male with a mean ±SD age of 60.3 ± 16.1 years old. The overall mortality rate was 26.2%. Poor prognostic factors included age over 65 years (HR = 4.03; 95%; CI: 1.27-12.76), cardiovascular disease (HR = 5.96; 95% CI: 1.98-17.92), receiving steroids (HR = 10.16; 95% CI: 2.27-45.47), not being treated (HR 4.81; 95% CI 1.12-20.67). Spoligotyping and DRE-PCR of the 48 MTB isolates revealed that 20 (41.7%) belonged to the Beijing family and 40 (83.3%) had a clustering pattern. Identification of a Beijing family isolate was not correlated with drug resistance or mortality. Clustering strains were likely to be resistant to isoniazid (OR = 4.71; 95% CI: 1.10 to 23.53). In this study of patients with urine culture-confirmed GUTB, age and coexisting diseases were independently associated with an unfavorable outcome. The Beijing family was the dominant genotype of GUTB isolates, but did not correlate with drug resistance or outcome.

Urogenital tuberculosis: patient classification in seven different groups according to clinical and radiological presentation

PURPOSE

To describe and classify 80 cases of urogenital tuberculosis in seven groups of similar clinical and radiological presentation.

MATERIALS AND METHODS

80 patients (56 males, 70%; median age 34 years; age range 12 to 75) with urogenital tuberculosis were retrospectively reviewed. The patients were divided in seven groups: 1) Bilateral parenchymatous renal lesions; 2) No or minimal changes on radiographic examination; 3) Unilateral renal tuberculosis; 4) Contracted bladder; 5) Contracted bladder with renal failure; 6) Tuberculosis on a transplanted kidney; 7) Isolated genital tuberculosis.

RESULTS

1) Seven (8.8%) patients had multiple bilateral parenchymatous renal lesions with fever and malaise, characteristic of miliary tuberculosis. Three of these patients had AIDS. 2) Six (7.5%) cases had an early diagnosis, with minimal or no radiographic lesions. Two did not have any urologic symptoms. 3) Twelve (15%) patients had unilateral renal tuberculosis with partial (1 case) or total non-function kidney. 4) Thirty-seven (46.3%) patients had contracted bladder associated with unilateral partial (1 case) or total non-function kidney. 5) Ten (12.5%) patients had end stage renal disease due to tuberculosis with contracted bladder. 6) Four (5.0%) patients had tuberculosis on a transplanted kidney, with graft loss in half the cases. 7) Four (5.0%) patients had prostate or epididymis tuberculosis without associated renal lesion.

CONCLUSIONS

Urogenital tuberculosis is a destructive disease of the urogenital tract with variable clinical and radiographic presentation. A classification according to similar patterns correlating with disease stage is feasible although early diagnosis is the only prevention of the most severe forms.

A better understanding of urogenital tuberculosis pathophysiology based on radiological findings

PURPOSE

To assess the radiological findings of urogenital tuberculosis (UGT) in patients at different disease stages, for a better understanding of its pathophysiology.

PATIENTS AND METHODS

We retrospectively reviewed the radiological exams of 20 men (median age 41 years; range: 28-65) with urogenital tuberculosis diagnosis. The patients were classified in the following groups: (1) bilateral renal tuberculosis with predominantly parenchymatous involvement; (2) unilateral renal tuberculosis; (3) unilateral renal tuberculosis with bladder tuberculosis and (4) bilateral renal tuberculosis with bladder tuberculosis.

RESULTS

One AIDS patient had multiple bilateral renal tuberculosis abscesses (group 1). Six patients had unilateral renal tuberculosis with hydronephrosis due to stenosis and thickening of the collecting system, without involvement of the bladder or contralateral kidney (group 2). Six patients had bladder tuberculosis with diffuse thickening of the bladder wall, with one very low or no function kidney while the other kidney was normal (group 3). Seven patients had bladder tuberculosis associated to a very low or no function kidney with the other kidney with high-grade vesicoureteral reflux-associated ureterohydronephrosis (group 4). In two patients, sequential exams showed evolution of tuberculosis from a unilateral renal and ureteral lesion to contracted bladder and dilatation of the contralateral kidney secondary to high-grade reflux.

CONCLUSIONS

UGT may have variable radiological presentations. However, in two of our cases we have seen that tuberculosis involvement of the urinary tract may be sequential. Further evidences are necessary to confirm this hypothesis.

Clinical features of confirmed versus suspected urogenital tuberculosis in region with extremely high prevalence of pulmonary tuberculosis

OBJECTIVES

To compare the characteristics of confirmed vs suspected cases of urogenital tuberculosis (UGTB) in a geographic region with an extremely high prevalence of pulmonary tuberculosis. UGTB is notoriously difficult to diagnose.

METHODS

A retrospective clinical record review was performed of 68 patients treated from March 1998 to July 2007. Group 1 (n = 45) had UGTB confirmed by microbiologic or histologic examination. Group 2 (n = 23) had a high suspicion of UGTB because of the clinical features, but no microbiologic or histologic confirmation. The data were collected and statistically analyzed using Student's t test for parametric data and Fisher's exact test for contingency tables (P < .05 was accepted as statistically significant).

RESULTS

The clinical characteristics were not significantly different statistically, except for flank pain (14% vs 43%), renal cavitation (14% vs 44%), urolithiasis (0% vs 25%), and ureteral stricture formation (7% vs 39%) in groups 1 and 2, respectively. Anti-TB medication was given to 7 patients (30%) in group 2 despite the lack of a confirmed diagnosis. The outcome in terms of complications and renal function loss was not significantly different between the 2 groups.

CONCLUSIONS

Flank pain, renal cavitation, urolithiasis, and ureteral stricture formation were significantly more common in the group with suspected UGTB than in those with confirmed UGTB. However, other clinical characteristics did not differ significantly between the 2 groups. In patients with clinical features highly suspicious of UGTB, it appears reasonable to institute anti-TB treatment, despite the lack of a confirmed diagnosis.

Surgical management of renal tuberculosis

Tuberculosis (TB) is one of the major health problems that our country is facing today. Despite active interventions by our government, control of TB still remains to be achieved. The emergence and exponential growth of the human immunodeficiency virus and drug-resistant strains threaten to further complicate the TB situation in our country. Even in this era of advanced chemotherapy, many lives are lost every day in our country. Tuberculosis of the urinary tract, despite being one of the commonest forms of extra-pulmonary TB, is generally overlooked. Most patients present with vague lower urinary symptoms typical of urinary tract infection. In this article, we shall highlight the various issues related to the surgical management of renal and ureteral tuberculosis.