Scanning Surveillance Research Articles

Scientific Opinion on the evaluation of molecular typing methods for major food-borne microbiological hazards and their use for attribution modelling, outbreak investigation and scanning surveillance: Part 2 (surveillance and data management activities)

Scientific Opinion on the evaluation of molecular typing methods for major food-borne microbiological hazards and their use for attribution modelling, outbreak investigation and scanning surveillance: Part 2 (surveillance and data management activities)

Scientific Opinion on the evaluation of molecular typing methods for major food‐borne microbiological hazards and their use for attribution modelling, outbreak investigation and scanning surveillance: Part 1 (evaluation of methods and applications)

An evaluation of molecular typing methods that can be applied to the food-borne pathogens Salmonella, Campylobacter, Shiga toxin-producing Escherichia coli and Listeria monocytogenes is presented. This evaluation is divided in two parts. Firstly, commonly used molecular typing methods are assessed against a set of predefined criteria relating to discriminatory capacity, reproducibility, repeatability and current or potential suitability for international harmonisation. Secondly, the methods are evaluated for their appropriateness for use in different public health-related applications. These applications include outbreak detection and investigation, attribution modelling, the potential for early identification of food-borne strains with epidemic potential and the integration of the resulting data in risk assessment. The results of these evaluations provide updated insights into the use and potential for use of molecular characterisation methods, including whole genome sequencing technologies, in microbial food safety. Recommendations are also made in order to encourage a holistic and structured approach to the use of molecular characterisation methods for food-borne pathogens; in particular, on the importance of structured co-ordination at international level to help overcome current limitations in harmonisation of data analysis and interpretation.

An observational study involving ewe postmortem examination at a fallen stock collection centre to inform flock health interventions

Effective sheep flock health plans must be underpinned by flock-specific diagnostic information and should make use of wider national flock health information. However, information on disease prevalence at flock level is often incomplete. This is despite the fact that protocols to diagnose common sheep diseases are well established and cost effective. Annual ewe mortality rates in the UK are estimated at 3–8 per cent (Johnston and others 1980, Scott 2007). The profile of diseases which contribute to mortality and involuntary culling in adult ewes in the UK flock is at present probably best estimated using Veterinary Investigation Diagnosis Analysis (VIDA) data (Gibbens and others 2008). This is generated by the Animal Health Veterinary Laboratories Agency (AHVLA) endemic disease scanning surveillance programme, which examines 500–700 ewes annually (VIDA 2012). However, the sample size, especially for carcases, is small, and the programme may have inherent biases (Nevel and Stark 2009) with under-representation of some important endemic diseases. By law, all fallen stock from UK farms must be collected for appropriate disposal by a licensed collector. This study aimed to investigate the diagnostic potential of this material, with an emphasis on adult ewes, and to consider how such information might be applied to improve sheep health, welfare and productivity. Between February 2012 and January 2013, a total of 106 adult ewes, collected from farms throughout the northeast of England, were examined postmortem during 11 sessions at a fallen stock collection centre. All postmortem examinations were performed by two experienced veterinary surgeons including at least one of the authors, whose competence in postmortem examination was gained during six years at …

Farm animal practitioners' views on their use and expectations of veterinary diagnostic laboratories

Diagnostic sampling of farm animals by private veterinary practitioners can be an important contributing factor towards the discovery of emerging and exotic diseases. This focus group study of farm animal...

A retrospective analysis of Salmonella serovars isolated from pigs in Great Britain between 1994 and 2010

A retrospective study analysing Salmonella serovars and antimicrobial resistance data from pigs in Great Britain between 1994 and 2010 was performed. Data were obtained through scanning surveillance and compared with prevalence data from other livestock species as well as human data. During the study period, two serovars, S. Typhimurium and S. Derby, predominated in British pigs. The total number of Salmonella incidents has decreased steadily over the study period, from 360 incidents per year in 1994 to 172 incidents in 2010. S. Typhimurium has been the most common serovar every year, but the relative percentage went down over the past few years. During the same time period, monophasic strains of S. Typhimurium have increased in numbers and were accounting for as much as 25% of incidents in 2010, representing the second most common serovar in British pigs in 2010. Antimicrobial resistance data from S. Typhimurium isolates show that the percentage of isolates which are resistant to six or more antimicrobials has increased from 27.2% in 1994 to 58.3% in 2010 and that the percentage of isolates fully sensitive to the panel of antimicrobials tested was only 3.3% in 2010. S. Typhimurium isolates belonged mainly to phagetypes DT193 and U288 in 2010, and an increase can be seen in the number of isolates belonging to phage type DT193. DT104, which was the predominant phagetype during the 1990s, has gone down considerably and represented less than 5% of all S. Typhimurium isolates in 2010. Monophasic strains of S. Typhimurium belonged mainly to phagetype 193 with less than 20% belonging to phagetype 120.The overall trend shows that the number of Salmonella incidents reported from British pigs has gone down considerably over the 17-year study period, but that the relative percentage of monophasic strains of S. Typhimurium has increased significantly. This trend seems to be in line with observations from other European countries, where an increase of this serovar can be seen both in livestock and in human patients. The increasing percentage of Salmonella-isolates which show multi-resistance is a matter of concern and has to be monitored carefully in order to assess any potential risks this may pose to human patients.

BVA leads veterinary input on the future of scanning surveillance

On January 23, around 30 representatives from the BVA's divisions and its Veterinary Policy Group took part in a workshop to discuss ways in which scanning surveillance could be improved in England and Wales.

Surveillance of bovine tuberculosis and risk estimation of a future reservoir formation in wildlife in Switzerland and Liechtenstein.

Bovine tuberculosis (bTB) caused by Mycobacterium bovis or M. caprae has recently (re-) emerged in livestock and wildlife in all countries bordering Switzerland (CH) and the Principality of Liechtenstein (FL). Comprehensive data for Swiss and Liechtenstein wildlife are not available so far, although two native species, wild boar (Sus scrofa) and red deer (Cervus elaphus elaphus), act as bTB reservoirs elsewhere in continental Europe. Our aims were (1) to assess the occurrence of bTB in these wild ungulates in CH/FL and to reinforce scanning surveillance in all wild mammals; (2) to evaluate the risk of a future bTB reservoir formation in wild boar and red deer in CH/FL. Tissue samples collected from 2009 to 2011 from 434 hunted red deer and wild boar and from eight diseased ungulates with tuberculosis-like lesions were tested by direct real-time PCR and culture to detect mycobacteria of the Mycobacterium tuberculosis complex (MTBC). Identification of suspicious colonies was attempted by real-time PCR, genotyping and spoligotyping. Information on risk factors for bTB maintenance within wildlife populations was retrieved from the literature and the situation regarding identified factors was assessed for our study areas. Mycobacteria of the MTBC were detected in six out of 165 wild boar (3.6%; 95% CI: 1.4–7.8) but none of the 269 red deer (0%; 0–1.4). M. microti was identified in two MTBC-positive wild boar, while species identification remained unsuccessful in four cases. Main risk factors for bTB maintenance worldwide, including different causes of aggregation often resulting from intensive wildlife management, are largely absent in CH and FL. In conclusion, M. bovis and M. caprae were not detected but we report for the first time MTBC mycobacteria in Swiss wild boar. Present conditions seem unfavorable for a reservoir emergence, nevertheless increasing population numbers of wild ungulates and offal consumption may represent a risk.

Investigation of the presence of ESBL‐producing Escherichia coli in the North Wales and West Midlands areas of the UK in 2007 to 2008 using scanning surveillance

Between November 5, 2007 and November 4, 2008, faecal samples from cattle and sheep submitted for diagnostic purposes to the Aberystwyth and Shrewsbury Veterinary Laboratories Agency (VLA) (now AHVLA) regional laboratories (covering North Wales and the West Midlands) were screened for the presence of Escherichia coli that produces CTX-M extended-spectrum β-lactamase (ESBL) using the selective medium CHROMagar CTX. Samples from 113 farms were tested and eight ESBL-positive farms identified. Of these, six farms were identified via submissions of cattle faeces and two from sheep. Gene sequencing revealed both group 1 and group 9 CTX-M enzymes corresponding to CTX-M-14, CTX-M-14B (group 9) and CTX-M-15/28 (group 1). Analysis of these isolates by nanoarray revealed that some were carrying a range of virulence genes including ireA, iroN and prfB, which have been associated with extraintestinal pathogenic E coli, and were multidrug resistant. Geographical analysis with choropleth maps suggested that these CTX-M genes are relatively widespread in the North Wales and West Midlands study area. This work was carried out concurrently with the running of a VLA ESBL surveillance system, which has subsequently identified many more CTX-M positive farms in the UK.

Emergence of suspected type D botulism in ruminants in England and Wales (2001 to 2009), associated with exposure to broiler litter

Scanning surveillance by the Veterinary Laboratories Agency revealed the emergence of suspected botulism in ruminants in 2003, presented as flaccid paralysis. From 2003 to 2009, 168 cattle and 19 sheep...

EPIZOOTIOLOGY AND PATHOLOGIC FINDINGS ASSOCIATED WITH A NEWLY DESCRIBED ADENOVIRUS IN THE RED SQUIRREL, SCIURUS VULGARIS

An infectious disease caused by Squirrelpox virus has contributed to the decline of red squirrels, Sciurus vulgaris, in the British Isles. Because of the heightened disease surveillance activity in red squirrels, adenovirus infection with associated mortality has been detected. Adenoviral disease is described in other rodent species usually associated with stressors. Here we 1) describe the pathologic findings in red squirrels found dead with adenoviral infection and gastrointestinal disease, and 2) investigate the epizootiology of the disease through pathologic investigation, scanning surveillance, and virologic studies. Ten red squirrels involved in conservation studies were diagnosed with adenoviral infection by electron microscopy or PCR. All squirrels exhibited diarrhea and small intestinal inflammation or hemorrhage was evident in seven cases. Lesions indicative of splenic lymphocytolysis were observed in one squirrel and leukocytic hepatitis in another. No adenovirus was detected in grey squirrels, Sciurus carolinensis, inhabiting the same forest area, but previous serologic studies showed that grey squirrels cannot be discounted as a reservoir of the virus. Scanning surveillance showed that 12% of 493 red squirrels had diarrheal disease and two of 13 free-living red squirrels with diarrheal disease had adenovirus infection. Adenoviral disease in declining free-living wild red squirrel populations in the British Isles occurs at a detectable frequency and its impact on the conservation of this species deserves further attention.

Modelling of extended objects using sparse multi-aspect High Range Resolution radar data set

The two-dimensional (2D) geometry of extended objects is modelled as a discrete constellation of a small number of scattering centres. Each scattering centre is characterised by its 2D location and extension, as well as by its observability from aspect angles spanning a wide angular interval. The considered input information of the modelling consists of high range resolution (HRR) data sets, which are measured by a network of scanning surveillance radars from a limited set of aspect angles of the object. During the short time-on-target of the antennas within each radar scan, inverse synthetic aperture radar (ISAR) imaging is performed. The Expectation-Maximisation (ER) algorithm is applied in order to fit each ISAR image to a Gaussian mixture model (GMM), pertaining to the aspect angle applicable to the respective radar. A merging algorithm for clustering all the partial GMMs into a unique 2D model of the extended object is designed. Cluster validation criteria are applied for correct alignment of the multi-radar multi-scan object model estimates. A Mixture of Gaussians classifier (MOGC), which is based on representation of each object by the estimated 2D model, is discussed. Results from application of the algorithms to two measured HRR radar data sets are presented.

Salmonella serovars and their antimicrobial resistance in British turkey flocks in 1995 to 2006

Serovar and antimicrobial resistance data from the scanning surveillance of British turkey flocks for Salmonella between 1995 and 2006 were analysed and compared with prevalence data from other livestock and animal feed. A total of 2753 incidents of 57 different serovars were reported. The five most prevalent serovars were Salmonella Typhimurium (20.8%), Salmonella Newport (14.7%), Salmonella Derby (10.6%), Salmonella Indiana (8.3%) and Salmonella Agona (6.4%). S. Typhimurium reports peaked in the mid- to late 1990s; this occurred in parallel with the S. Typhimurium DT104 epidemic in other livestock species. S. Enteritidis reports peaked in mid- to late 1990s, followed by a considerable decrease after 2000, which was also noted in flocks of domestic fowl. S. Newport, Salmonella Montevideo, Salmonella Senftenberg and Salmonella Binza occurred in marked clusters, indicating that they were introduced into one or more flocks at a certain time (i.e. via contaminated feed or infected 1-day-old chicks). A proportion of 43.1% of the reported Salmonella isolates were resistant to at least one antimicrobial, while 17.7% were multi-resistant. No isolates were resistant to ciprofloxacin or to the third-generation cephalosporins ceftazidime and cefotaxime. Resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide compounds and tetracycline was common, and it was mainly a characteristic of S. Typhimurium DT104 compared with S. Typhimurium non-DT104 and non-S. Typhimurium isolates (P<0.001). Resistance to nalidixic acid decreased from 16.9% in 1995 to 11.8% in 2006. Nalidixic acid resistance was most frequently found in Salonella Hadar (71.4%), S. Typhimurium DT104 (30.0%), S. Newport (17.9%) and S. Typhimurium non-DT104 (11.1%).

Endovascular treatment of internal iliac artery obstructive disease

This study evaluated the therapeutic value of endovascular techniques in patients with buttock claudication caused by stenosis or occlusion of the internal iliac artery. The records of patients with buttock claudication who had undergone endovascular treatment for internal iliac artery stenosis or occlusion were analyzed retrospectively, and any associated arterial lesions, morbidity, restenosis, or recurrent buttock claudication was noted. Outcomes were compared with published reports. Iliac artery duplex scans and aortoiliac angiography were performed to detect and confirm the internal iliac artery obstructive disease. The iliac duplex scanning surveillance protocol was set at 3, 6, and 12 months and yearly thereafter to detect eventual restenosis or occlusion. Between September 2006 and September 2008, 21 consecutive patients (19 men; mean age, 67 years) with 22 cases of buttock claudication (1 bilateral localization) underwent percutaneous transluminal angioplasty alone (14 cases) or additional stent placement in case of elastic recoil (8 cases). Buttock claudication was associated with impotence, thigh claudication, or calf claudication in seven patients. The endovascular approach was successful in all patients, without morbidity or mortality. During a mean follow-up of 14.7 +/- 5.7 months, 50% restenosis occurred in one 80-year-old patient. The patient had a pain-free walking distance of 110 meters and was treated conservatively. To our knowledge, the present study is the largest published report concerning endoluminal treatment of buttock claudication due to internal iliac artery obstructive disease. The midterm results are very encouraging and underscore the value of stent-supported angioplasty as first-line treatment. The procedure can be repeated should significant restenosis occur and does not compromise the option of surgical repair of the lesions.

Poxviral Disease in Red Squirrels Sciurus vulgaris in the UK: Spatial and Temporal Trends of an Emerging Threat

The squirrel poxvirus (SQPV) is the probable mediator of apparent competition between the introduced invading gray squirrel (Sciurus carolinensis) and the red squirrel (Sciurus vulgaris) in the UK, and modeling studies have shown that this viral disease has had a significant impact on the decline of the red squirrel in the UK. However, given our limited understanding of the epidemiology of the disease, and more generally the effects of invasive species on parasite ecology, there is a need to investigate the transmission dynamics and the relative pathogenicity of the virus between species. We aimed to increase our knowledge of these processes through an empirical study in which we: (i) used pathological signs and transmission electron microscopy (TEM) to diagnose SQPV disease in red squirrels found dead during scanning surveillance between 1993 and 2005; (ii) detected antibody to SQPV using an enzyme-linked immunosorbent assay (ELISA) in the same animals; and (iii) mapped cases of the disease, and the gray squirrel distribution, using a geographical information system. We analyzed the distribution of cases of SQPV disease according to woodland type, a measure of squirrel density. SQPV disease occurred only in areas of England also inhabited by seropositive gray squirrels, and as the geographical range of gray squirrels expanded, SQPV disease occurred in these new gray squirrel habitats, supporting a role for the gray squirrel as a reservoir host of the virus. There was a delay between the establishment of invading gray squirrels and cases of the disease in red squirrels which implies gray squirrels must reach a threshold number or density before the virus is transmitted to red squirrels. The spatial and temporal trend in SQPV disease outbreaks suggested that SQPV disease will have a significant effect on Scottish populations of red squirrels within 25 years. The even spread of cases of disease across months suggested a direct rather than vector-borne transmission route is more likely. Eight juvenile and sub-adult free-living red squirrels apparently survived exposure to SQPV by mounting an immune response, the first evidence of immunity to SQPV in free-living red squirrels, which possibly suggests a changing host-parasite relationship and that the use of a vaccine may be an effective management tool to protect remnant red squirrel populations.

The Influence of Routine Duplex Scanning Surveillance on Outcome after Percutaneous Iliac Angioplasty and Stenting

Purpose We sought to determine the utility of noninvasive color-flow duplex imaging (CDI) in the detection of iliac artery stenoses or occlusions and correlate the findings of long-term color flow duplex surveillance (CFDS) to clinical outcome after percutaneous iliac interventions. Methods All patients undergoing percutaneous iliac angioplasty and stenting are prospectively entered in a surveillance protocol with CFDS and ankle-brachial indices (ABIs) performed within 6 weeks, 6 months, 12 months, and every year thereafter. Preprocedural ABI and peak systolic velocity (PSV) values were compared with postprocedural values with the Student t-test. Kaplan-Meier life-table analysis was used to estimate the patency rates. Results During the last 4 years, 80 patients with 112 treated iliac systems fulfilled the study criteria. A total of 68 patients (84%) had claudication, 8 (10%) had pain at rest, and 5 (6%) had a nonhealing ulcer or gangrene. The procedural success rate was 96.4%. Comparison of ABIs and PSV values before and after iliac intervention was statistically significant ( p &lt; 0.0001). Duplex scan allowed the detection and/or monitoring of abnormal velocities in 14 treated iliac arteries. Four cases (3.5%) required reintervention on previously treated iliac arteries for symptomatic restenosis and/or disease progression. Late stent occlusions were correctly identified in two cases. Primary patency, assisted primary patency, and secondary patency rates were 77%, 94%, and 96% at 4 years, respectively. Conclusion CFDS allows the detection of iliac artery stenoses and is a useful tool to identify restenosis after intervention. Because of the overall excellent patency rates observed with iliac angioplasty and stenting, CFDS surveillance in the absence of symptoms may not always be necessary and its long-term use should be individualized.

Repair of Anastomotic Abdominal Aortic Pseudoaneurysm Utilizing Sequential AneuRx Aortic Cuffs in an Overlapping Configuration

Anastomotic aortic pseudoaneurysm is a known late complication following aortic repair and presents a considerable surgical challenge. We herein evaluate the endovascular alternative of using sequential AneuRx aortic cuffs to bridge the degenerative anastomotic pseudoaneurysms as a definitive treatment. Over a 3-year period, six patients with a mean age of 68.7 years (range 58-75) were identified who had proximal anastomotic aortic pseudoaneurysms secondary to previously implanted bifurcated aortic grafts (mean 15, range 12-20 years) following open surgical correction of aortoiliac occlusive disease. Five patients (83%) presented with concomitant palpable femoral anastomotic pseudoaneurysms and one patient (16%) had a pulsatile abdominal mass. All patients had computed tomographic (CT) scans confirming proximal anastomotic pseudoaneuryms without evidence of infection. The mean diameter of the pseudoaneurysms was 5.3 cm (range 4.0-7.0). Five patients were treated with endovascular methods, while one patient was not suitable for endovascular repair due to the diameter of the native aorta as seen on imaging study at the time of the procedure. AneuRx aortic extender cuffs (3.75 cm length) were deployed sequentially in five patients via a femoral approach. Devices were overlapped approximately 1.5 cm in order to achieve total exclusion of the pseudoaneurysms, and all concomitant femoral aneurysms were repaired surgically at the same time. Successful exclusion of the anastomotic pseudoaneurysm was achieved in four patients (80%) using a combination of two or three overlapping aortic cuffs. One patient had a small residual endoleak that had sealed by 1 month, evidenced by follow-up CT. The renal arteries were preserved in all patients. The average estimated blood loss and operative time were 355 +/- 25 cc and 84 +/- 21 min, respectively. The average length of hospital stay was 2.1 days, and there was no mortality or major morbidity. All patients underwent CT scanning surveillance at 6 and 12 months and yearly afterward. There was no evidence of late endoleak, aneurysmal expansion, or device migration during the mean follow-up of 10 months, ranging 6-27 months. Our study demonstrated that utilizing sequential AneuRx aortic cuffs applied in an overlapping configuration is an effective strategy for degenerative aortic anastomotic pseudoaneurysm from previously placed aortic grafts. Additionally, our study suggests this unique endovascular technique is an ideal alternative for creating a customized tube graft in challenging cases, particularly in high-risk patients.

Disease Progression in the Contralateral Carotid Artery after Endarterectomy

Our objectives were to establish the incidence and progression of stenotic lesions in the contralateral carotid artery (CCA) after endarterectomy, to identify subpopulations of patients at risk of contralateral disease progression, and to evaluate the efficacy of duplex scanning surveillance at detecting these lesions. We performed a prospective study on 180 patients in whom the CCA to the operated artery was healthy or showed <70% stenosis. All patients had completed a clinical and hemodynamic follow-up program, including duplex scanning of both carotids, with sessions 3 and 6 months after surgery and then every semester until 2 years. Thereafter, examinations were scheduled according to the severity of stenosis. Mean follow-up time was 26.2 months (range 1.6-67.6). Disease progression was observed in 26 lesions (15%), nine of which (5.5%) progressed to severe stenosis (SS). Kaplan-Meier event-free rates of any disease progression were 89%, 88%, 82%, and 79% for 1, 2, 3, and 4 years, respectively. Event-free rates of progression to SS were 98%, 96%, 93%, and 90.6%, respectively, for 1, 2, 3, and 4 years. The risk of progression to SS was five times higher for stenoses that were moderate at the start of the study (p = 0.025). Severe contralateral stenoses were more common and appeared later during follow-up than ipsilateral restenoses. Progression of contralateral stenotic lesions is not uncommon and is essentially related to the presence of a moderate lesion at the start of follow-up. Indeed, moderate stenosis is a risk factor for progression to SS, which appears later and more frequently than ipsilateral restenosis. It therefore seems that patients with a moderate contralateral lesion would benefit from long-term duplex ultrasound surveillance.

Disease progression in contralateral carotid artery is common after endarterectomy.

Although the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) have helped to define the role of carotid endarterectomy (CEA) for both symptomatic and asymptomatic lesions, the role of surveillance of the contralateral carotid artery remains unclear. The purpose of this study was to determine the progression of contralateral carotid artery disease with serial duplex ultrasound scans after CEA compared with the recurrent stenosis rate for the carotid artery ipsilateral to the CEA. From January 1990 to December 2000, 473 CEA procedures were performed at a Veterans Affairs Medical Center. From this group we identified 279 patients who had undergone first-time CEA, as well as preoperative duplex scanning and postoperative duplex scanning at least once, in the vascular laboratory. At each visit stenosis of the internal carotid artery (ICA) was categorized as none (0%-14%), mild (15%-49%), moderate (50%-79%), severe (80%-99%), or occluded. Analysis of probability of freedom from progression was determined. Progression was defined as an increase in ICA stenosis 50% or greater or increase to a higher category of stenosis if baseline was 50% or greater. The Cox proportional hazards model was used for data analysis. Mean patient age was 65.7 years (range, 33-100 years). The 1024 carotid duplex ultrasound scanning examinations performed (mean, 3.7; range, 2-13) included the last study done before the index CEA and all studies done after the CEA. Mean follow-up was 27 months (range, 1-137 months). Forty-six patients were found to have contralateral carotid occlusion at initial duplex scanning, and were therefore excluded from the contralateral progression analysis. Contralateral progression was more frequent than ipsilateral recurrent stenosis at long-term follow-up (P <.01). Annual rates of "any progression" and "progression to severe stenosis or occlusion" were 8.3% and 4.4%, respectively, for contralateral arteries, and 4.3% and 2.4%, respectively for ipsilateral arteries. As a result of surveillance, 43 contralateral CEAs (19% of initial cohort) were performed. Carotid stenosis regressed in 25 arteries (10.7%). Baseline clinical and demographic factors did not predict disease progression. Baseline contralateral stenosis did not predict time to "any progression," but was a strong predictor of "progression to severe stenosis or occlusion" (P <.001). After CEA, we identified an 8.3% annual rate of progression of contralateral carotid artery stenosis and a 4.4% annual rate of progression to severe stenosis or occlusion. Baseline contralateral stenosis was significantly predictive of progression to severe stenosis or occlusion. Clinical and demographic factors were not helpful in predicting which patients would have disease progression. These data may help in assessing the cost effectiveness of duplex scanning surveillance after CEA.

Long-term outcome of revised lower-extremity bypass grafts

Purpose: Reversed lower-extremity vein grafts (LEVGs) frequently require operative revisions to maintain patency. Identifying grafts that are at risk, however, requires an intensive duplex scanning-based surveillance program. Excellent 5-year graft patency and limb-salvage rates have previously been reported in patients undergoing graft revisions, but results beyond 5 years are essentially unknown, a factor that is of importance in an increasingly aging population. This study was performed to determine the results of surgical revisions of LEVGs after a follow-up as long as 10 years. Methods: All patients undergoing placement of a LEVG were observed in a program of duplex scanning-based surveillance as long as the patient remained a candidate for graft revision. Grafts were considered for revision on the basis of the presence of focal areas of increased velocity, a prestenotic to intrastenotic velocity ratio more than 3.0, or uniformly low velocities throughout the graft. All lesions were confirmed with preoperative arteriography before revision. Assisted primary patency, limb-salvage, and survival rates were determined by means of Kaplan-Meier analysis in all patients who underwent LEVG revision from January 1990 to December 2000. Results: A total of 1498 LEVG procedures were performed during the study period. A total of 330 surgical graft revisions were performed on 259 extremities in 245 patients. The median follow-up period was 38 months. The assisted primary patency rate of all grafts, the limb-salvage rate for patients undergoing surgery for limb-salvage indications, and the survival rate of all patients were 87.4%, 88.7%, and 72.4%, respectively, 5 years after the original bypass grafting procedure, 85.7%, 83.4%, and 67.8%, respectively, 7 years after the original bypass grafting procedure, and 80.4%, 75.4%, and 53.4%, respectively, 10 years after the original bypass grafting procedure. A total of 180 revisions (55%) were performed during the first year, 110 (33%) between the first year and the fifth year, and 40 revisions (12%) were performed on grafts older than 5 years. LEVGs revised within the first year after bypass grafting had lesions within the graft in 78%, in the native arterial inflow in 10%, and in the native arterial outflow in 12%. This differed significantly from the location of lesions in revisions performed between 1 and 5 years and after 5 years (graft, 63% and 62%; inflow, 20% and 19%; outflow, 17% and 19%; P >.05, Chi-square). Conclusion: Excellent assisted primary patency and limb-salvage rates can be achieved for as long as 10 years in LEVGs that require revision, with only a 7% drop in overall patency and limb-salvage rates between the fifth and 10th years. Although most revisions were required within the first year, 34% were performed between the first year and the fifth year, and 11% after 5 years. These data support the growing body of evidence that favors an aggressive regimen of duplex scanning surveillance of LEVGs for the life of the graft. Revised grafts have excellent patency through 10 years. (J Vasc Surg 2002;35:56-63.)

Automatic signal detection applied to fire control by infrared digital signal processing

This paper presents a general scheme for automatic signal detection in scanning surveillance systems. It considers the problem of deciding whether an alert situation exists, based on the data measured in the cell under analysis in different consecutive scanning time instants. The proposed scheme includes a linear predictor and a subspace model for the signal to be detected, in an attempt to maximise the performance of the detector. Although this system may be applicable to general scanning surveillance problems, we focus the work on the problem of wide-area uncontrolled fire detection by means of infrared radar.