Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “NORTH AMERICA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2006

Prevalence and antimicrobial susceptibility patterns among gastroenteritis-causing pathogens recovered in Europe and Latin America and Salmonella isolates recovered from bloodstream infections in North America and Latin America: report from the SENTRY Antimicrobial Surveillance Program (2003).

Gastroenteritis-causing pathogens are the second leading cause of morbidity and mortality worldwide. Complicating the clinical diarrhoea syndrome is the emergence of antimicrobial resistance among the responsible bacterial pathogens. The reported increases in fluoroquinolone resistance in Salmonella, Shigella and Campylobacter have been extremely worrisome considering the primary role of ciprofloxacin as a treatment. In this study, 1479 bacterial isolates from gastroenteritis infections were collected in Europe and Latin America, which included Salmonella spp. (834; 56%), Shigella spp. (311; 21%), Campylobacter spp. (182; 12%) and Aeromonas spp. (72; 5%). The fluoroquinolones displayed the greatest activity against these pathogens, with only three non-Campylobacter spp. strains being non-susceptible using current Clinical and Laboratory Standards Institute (CLSI) breakpoint criteria. Whilst ciprofloxacin resistance in European and Latin American Salmonella was only 0.2% and 0.0%, respectively, a total of 16.2% and 12.9% of isolates were resistant to nalidixic acid, indicating possible first-step gyrA mutations. Among confirmed extended-spectrum beta-lactamase-producing Salmonella strains, CTX-M genes were detected in 15 originating from Russia. Erythromycin and azithromycin were the most potent agents tested against Campylobacter spp. (values of minimum inhibitory concentration for 90% of the organisms, 0.5 mg/L and 0.12 mg/L, respectively), with erythromycin displaying the highest susceptibility (91.1%). Salmonella isolates from bloodstream infections displayed antibiograms that were nearly identical to strains causing gastroenteritis. Considering the role that antimicrobial therapy plays in the management of moderate to severe bacterial gastroenteritis, global surveillance and local/national public health programmes can provide critical data illuminating the dissemination of resistance and guidance for empirical therapy.

Aeromonas↗
PubMed2007

Response to host volatiles by native and introduced populations of Dendroctonus valens (Coleoptera: Curculionidae, Scolytinae) in North America and China.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) have specialized feeding habits, and commonly colonize only one or a few closely related host genera in their geographical ranges. The red turpentine beetle, Dendroctonus valens LeConte, has a broad geographic distribution in North America and exploits volatile cues from a wide variety of pines in selecting hosts. Semiochemicals have been investigated for D. valens in North America and in its introduced range in China, yielding apparent regional differences in response to various host volatiles. Testing volatiles as attractants for D. valens in its native and introduced ranges provides an opportunity to determine whether geographic separation promotes local adaptation to host compounds and to explore potential behavioral divergence in native and introduced regions. Furthermore, understanding the chemical ecology of host selection facilitates development of semiochemicals for monitoring and controlling bark beetles, especially during the process of expansion into new geographic ranges. We investigated the responses of D. valens to various monoterpenes across a wide range of sites across North America and one site in China, and used the resulting information to develop an optimal lure for monitoring populations of D. valens throughout its Holarctic range. Semiochemicals were selected based on previous work with D. valens: (R)-(+)-alpha-pinene, (S)-(-)-alpha-pinene, (S)-(-)-beta-pinene, (S)-(+)-3-carene, a commercially available lure [1:1:1 ratio of (R)-(+)-alpha-pinene:(S)-(-)-beta-pinene:(S)-(+)-3-carene], and a blank control. At the release rates used, (+)-3-carene was the most attractive monoterpene tested throughout the native range in North America and introduced range in China, confirming results from Chinese studies. In addition to reporting a more effective lure for D. valens, we present a straightforward statistical procedure for analysis of insect trap count data yielding cells with zero counts, an outcome that is common but makes the estimation of the variance with a Generalized Linear Model unreliable because of the variability/mean count dependency.

Animals↗
PubMed1999

Late quaternary extinction of a tree species in eastern North America.

Widespread species- and genus-level extinctions of mammals in North America and Europe occurred during the last deglaciation [16,000-9,000 yr B.P. (by (14)C)], a period of rapid and often abrupt climatic and vegetational change. These extinctions are variously ascribed to environmental change and overkill by human hunters. By contrast, plant extinctions since the Middle Pleistocene are undocumented, suggesting that plant species have been able to respond to environmental changes of the past several glacial/interglacial cycles by migration. We provide evidence from morphological studies of fossil cones and anatomical studies of fossil needles that a now-extinct species of spruce (Picea critchfieldii sp. nov.) was widespread in eastern North America during the Last Glacial Maximum. P. critchfieldii was dominant in vegetation of the Lower Mississippi Valley, and extended at least as far east as western Georgia. P. critchfieldii disappeared during the last deglaciation, and its extinction is not directly attributable to human activities. Similarly widespread plant species may be at risk of extinction in the face of future climate change.

Biological Evolution↗
PubMed2004

Assessment of pathogen occurrences and resistance profiles among infected patients in the intensive care unit: report from the SENTRY Antimicrobial Surveillance Program (North America, 2001).

Originating from 25 selected intensive care units (ICUs) in North America, a total of 1,321 bacterial strains from blood, respiratory tract, urine and wound sites were processed at a central laboratory as part of the SENTRY Antimicrobial Surveillance Program (2001) to assess their occurrence rates and antimicrobial susceptibility profiles. The rank order of pathogens recovered was Staphylococcus aureus (24.1%), Pseudomonas aeruginosa (12.2%), Escherichia coli (10.1%), Klebsiella spp. (8.9%), Enterococcus spp. (7.2%), coagulase-negative staphylococci (7.0%) and Enterobacter spp. (7.0%). Although oxacillin resistance among S. aureus was 51.4%, no resistance was detected to vancomycin, linezolid and quinupristin/dalfopristin. The most active agents tested against P. aeruginosa were amikacin, cefepime, tobramycin, meropenem and piperacillin/tazobactam (3.1-13.0% resistance). Among agents tested against the Enterobacteriaceae, amikacin, cefepime, imipenem and meropenem showed greatest in vitro activity (0.0-3.4% resistance). Extended-spectrum beta-lactamase-producing phenotype rates were 11.2 and 16.2% in E. coli and Klebsiella spp., respectively. Linezolid was most active against enterococci (1.1% resistance; G2576U ribosomal mutation) whereas 28.4% of isolates were resistant to vancomycin. Cefepime and the carbapenems (imipenem or meropenem) for Gram-negative isolates and linezolid for Gram-positive isolates, provided the broadest spectrum of in vitro activity against contemporary ICU pathogens in North America.

Anti-Bacterial Agents↗
PubMed1999

Environmental imperatives reconsidered: demographic crises in western North America during the medieval climatic anomaly.

Review of late Holocene paleoenvironmental and cultural sequences from four regions of western North America show striking correlations between drought and changes in subsistence, population, exchange, health, and interpersonal violence during the Medieval Climatic Anomaly (A.D. 800-1350). While ultimate causality is difficult to identify in the archaeological record, synchrony of the environmental and cultural changes and the negative character of many human responses--increased interpersonal violence, deterioration of long-distance exchange relationships, and regional abandonments--suggest widespread demographic crises caused by decreased environmental productivity. The medieval droughts occurred at a unique juncture in the demographic history of western North America when unusually large populations of both hunter-gathers and agriculturalists had evolved highly intensified economies that put them in unprecedented ecological jeopardy. Long-term patterns in the archaeological record are inconsistent with the predicted outcomes of simple adaptation or continuous economic intensification, suggesting that in this instance environmental dynamics played a major role in cultural transformations across a wide expanse of western North America among groups with diverse subsistence strategies. These events suggest that environment should not be overlooked as a potential cause of prehistoric culture change.

Climate↗
PubMed1982

Status of farm animal behavioral research in North America.

To evaluate the current status of farm animal behavioral research in North America, we searched and analyzed the scientific literature, consulted the national Agricultural Library and the Current Research Information System of the USDA and sought advice from several authorities. We than sent letters to 78 North American behavioral researchers, inviting them to supply information about their current projects and recently completed studies. A total of 218 efforts were identified. A quantitative and qualitative summary of current behavioral research and short reviews of selected references are provided to illustrate the broad range of current farm animal behavioral research in North America.

Agriculture↗
PubMed2001

Dipteronia (Sapindaceae) from the Tertiary of North America and implications for the phytogeographic history of the Aceroideae.

The fossil record of Dipteronia, the sister genus of Acer, is reviewed based on diagnostic winged fruits from the Tertiary of western North America. Today the genus is endemic to eastern Asia with two extant species in central and southern China, but it is well represented in the Tertiary of western North America, ranging from the Paleocene to the Oligocene with the greatest number of occurrences in the middle to late Eocene. There are no known fossil occurrences outside of North America. The fossil fruits, assigned to the new species D. brownii sp. nov., are smaller than those of both living species and were tricarpellate as well as bicarpellate in contrast to the modern species, which are almost exclusively bicarpellate. The tricarpellate condition may be plesiomorphic for Dipteronia and perhaps Aceroideae. The area of origin for Dipteronia is unknown, but it seems likely to have been either Asia or North America, with the genus crossing Beringia in the Paleogene.

Journal Article↗
PubMed2006

Evolution of rattlesnakes (Viperidae; Crotalus) in the warm deserts of western North America shaped by Neogene vicariance and Quaternary climate change.

During Pleistocene, the Laurentide ice sheet rearranged and diversified biotic distributions in eastern North America, yet had minimal physical impact in western North America where lineage diversification is instead hypothesized to result from climatic changes. If Pleistocene climatic fluctuations impacted desert species, the latter would reflect patterns of restricted gene flow concomitant with indications of demographic bottlenecks. Accordingly, molecular evidence for refugia should be present within these distributions and for subsequent range expansions as conditions improved. We sought answers to these questions by evaluating mitochondrial DNA (mtDNA) sequences from four species of rattlesnakes [Crotalus mitchellii (speckled rattlesnake), Crotalus cerastes (sidewinder), Crotalus tigris (tiger rattlesnake), Crotalus ruber (red diamond rattlesnake)] with distributions restricted to desert regions of southwestern North America. We inferred relationships using parsimony and maximum likelihood, tested intraspecific clades for population expansions, applied an isolation-with-migration model to determine bi-directional migration rates (m) among regions, and inferred divergence times for species and clades by applying a semiparametric penalized likelihood approach to our molecular data. Evidence for significant range expansion was present in two of eight regions in two species (Crotalus mitchellii pyrrhus, C. tigris region north). Two species (C. cerastes, C. mitchellii) showed a distribution concomitant with northward displacement of Baja California from mainland México, followed by vicariant separation into subclades. Effects of Pleistocene climate fluctuations were found in the distributions of all four species. Three regional diversification patterns were identified: (i) shallow genetic diversity that resulted from Pleistocene climatic events (C. tigris, C. ruber); (ii) deep Pleistocene divisions indicating allopatric segregation of subclades within refugia (C. mitchellii, C. cerastes); and (iii) lineage diversifications that extended to Pliocene or Late Miocene (C. mitchellii, C. cerastes). Clade-diversifying and clade-constraining effects impacted the four species of rattlesnakes unequally. We found relatively high levels of molecular diversification in the two most broadly distributed species (C. mitchellii, C. cerastes), and lower levels of genetic diversification in the two species (C. tigris, C. ruber) whose ranges are relatively more restricted. Furthermore, in several cases, the distributions of subspecies were not congruent with our molecular information. We suggest regional conservation perspectives for southwestern deserts cannot rely upon subspecies as biodiversity surrogates, but must instead employ a molecular and deep historical perspective as a primary mechanism to frame biodiversity reserves within this region.

Adenosine Triphosphatases↗
PubMed1991

Tick paralysis in North America and Australia.

The pathophysiology and clinical manifestations of tick paralysis in North America and Australia are reviewed. Clinical and electrodiagnostic findings in tick paralysis are contrasted with those that occur in other diffuse lower motor neuron disorders, and the disease in North America is compared with the more severe form of the disease that occurs along the east coast of Australia. A detailed account of the treatment of animals afflicted with tick paralysis is presented.

Animals↗
PubMed2005

Evidence of hybridization between Lythrum salicaria (purple loosestrife) and L. alatum (winged loosestrife) in North America.

BACKGROUND AND AIMS: Although Lythrum salicaria (purple loosestrife) was introduced to North America from Europe in the early 1800s, it did not become invasive until the 1930s. Whether hybridization with L. alatum (winged loosestrife) could have played a role in its ultimate spread was tested. METHODS: Six diagnostic morphological traits (flower number per axil, leaf placement, calyx pubescence, style type, plant height and leaf shape) were surveyed in 30 populations of Lythrum across eastern North America. Patterns of AFLP variation were also evaluated using five primer pairs in a 'global screen' of the same North American populations of L. salicaria and L. alatum described above, in L. salicaria from 11 European populations located in Germany, England, Ireland, Austria and Finland, and in six L. salicaria cultivars. KEY RESULTS: All of the North American L. salicaria populations had individuals with alternate leaf placement and 1-2 flowers per leaf axil, which have not been described in Eurasian L. salicaria but predominate in North American L. alatum. In addition, two L. salicaria populations were intermediate in height and leaf ratio between the typical L. salicaria and L. alatum populations in their native fields and when grown in a common greenhouse. In screens of variation patterns using 279 AFLPs, only two fragments were found that clearly supported introgression from L. alatum to L. salicaria. CONCLUSIONS: The evidence indicates that L. salicaria may have hybridized with L. alatum, but if so, only a small fraction of L. alatum genes have been retained in the genome of L. salicaria. This is unlikely to have led to a dramatic adaptive shift unless the introgression of a few key genes into L. salicaria stimulated a genomic reorganization. It is more likely that crossing among genotypes of L. salicaria from multiple introductions provided the necessary variability for new adaptations to arise.

Body Size↗
PubMed2006

Eastern North America as an independent center of plant domestication.

The status of eastern North America as an independent center of plant domestication has recently been called into question by a number of genetic and archaeological studies, which suggest that the region may not have witnessed the independent domestication of local crop plants, but rather may have been on the receiving end of domesticated crop plants introduced from Mexico. Here, I provide a synthesis of the currently available archaeological and genetic evidence from both eastern North America and Mexico regarding the spatial and temporal context of initial domestication of the four plant species identified as potential eastern North American domesticates: marshelder (Iva annua), chenopod (Chenopodium berlandieri), squash (Cucurbita pepo), and sunflower (Helianthus annuus). Genetic and archaeological evidence provides strong support for the independent domestication of all four of these plant species in the eastern United States and reconfirms the region as one of the world's independent centers of domestication.

Agriculture↗
PubMed2002

The epidemiology and natural history of Crohn's disease in population-based patient cohorts from North America: a systematic review.

AIM: To quantify, through systematic review, the epidemiology and natural history of Crohn's disease in North America. METHODS: The selected articles contained: (i) population-based samples of patients followed from the time of diagnosis; and (ii) objective diagnostic criteria for disease. Studies on the natural history of Crohn's disease also contained sufficient follow-up. DATA COLLECTION AND ANALYSIS: For prevalence studies, data on the incidence, prevalence, gender and age at diagnosis were extracted. For natural history studies, data on the disease activity, use of medications and surgery were extracted. MAIN RESULTS: The prevalence of Crohn's disease in North America ranges from 26.0 to 198.5 cases per 100,000 persons. The incidence rates range from 3.1 to 14.6 cases per 100,000 person-years. Most patients have a chronic intermittent disease course, while 13% have an unremitting disease course and 10% have a prolonged remission. Less than half require corticosteroids at any point. During any given year, approximately 10% are treated with corticosteroids and 30% are treated with 5-aminosalicylates. Up to 57% of patients require at least one surgical resection. CONCLUSIONS: Between 400,000 and 600,000 patients in North America have Crohn's disease, and the natural history is marked by frequent exacerbations requiring treatment with corticosteroids, 5-aminosalicylate products and surgery.

Adolescent↗
PubMed1988

Biological and cultural sources of familial resemblance in plasma lipids: a comparison between North America and Israel--the Lipid Research Clinics Program.

Heterogeneity in determinants of familial resemblance of lipid and lipoprotein levels between populations in North America and Israel was investigated using path analysis. A common protocol, identical measurement techniques, and the same statistical procedures were used in the two samples. Both genetic (h2) and cultural (c2) determinants of inheritance were significant for all lipid variables in the two studies. Genetic and cultural heritability of total cholesterol (h2 = 0.61, c2 = 0.02), low-density lipoprotein cholesterol (h2 = 0.59, c2 = 0.02), and high-density lipoprotein cholesterol (h2 = 0.55, c2 = 0.06) did not differ significantly between North America and Israel, while there was a significant difference for triglyceride (h2 = 0.41, c2 = 0.07 in North America; h2 = 0.61, c2 = 0.05 in Israel). Secondary parameters of the path model describing intrafamilial environmental relationships differed between the two countries. In particular, there was a higher correlation between marital environments in Israel for all traits except triglyceride, and a larger effect of father's environment on offspring's environment in Israel for all traits. Within both populations, variation of plasma lipids and lipoproteins was mostly explained by genetic factors and random unmeasured environmental factors. The contribution of common family environment was found to be small, though statistically significant. This is probably due to homogeneity of the distribution of familial environmental determinants within both countries.

Cholesterol↗
PubMed2006

Declining growth rate of West Nile virus in North America.

To determine the demographic history of West Nile virus (WNV) in North America, we employed a coalescent method to envelope coding region data sets for the NY99 and WN02 genotypes. Although the observed genetic diversities in both genotypes were of approximately the same age, the mean rate of epidemiological growth of the WN02 population was approximately three times that of the NY99 population, a finding compatible with the recent dominance of the former genotype. However, there has also been a marked decrease in the recent growth rate of WN02, suggesting that WNV has reached its peak prevalence in North America.

Animals↗
PubMed2005

The history and geography of diversification within the butterfly genus Lycaeides in North America.

The Lycaeides butterfly species complex in North America consists of two nominal, morphologically defined species. These butterflies are ecologically diverse and appear to be distributed as a geographically complex mosaic of locally differentiated populations that may be undergoing adaptive radiation. We asked whether patterns of molecular genetic variation within the species complex are congruent with currently recognized morphological species and whether the distribution of molecular variation is consistent with the hypothesis that Pleistocene climate changes contributed to the process of differentiation within the genus. Variation in the form of the genitalia from 726 males from 59 populations clearly distinguishes both species with only six populations containing morphologically intermediate or ambiguous individuals. However, partitioning of molecular variance in a 236 bp section of the mitochondrial AT-rich region from 628 individuals (57 populations) surveyed using single strand conformation polymorphism analysis (SSCP) indicates that only 26% of the total genetic variation is distributed along nominal species boundaries as defined by morphology. Instead, three phylogeographical groups were detected, represented by three major haplotype clades, which account for 90% of the total genetic variance. Pleistocene glaciations appear to have fostered divergence during glacial maxima, while post-glacial range expansions created opportunities for gene exchange and reticulation along suture zones between geographical groups. Data presented here allow us to make inferences about the history of the species complex. However, evidence of ancestral polymorphism and reticulation limit our ability to define species boundaries based on mitochondrial DNA sequence variation.

Analysis of Variance↗
PubMed2006

Comparative phylogeography of unglaciated eastern North America.

Regional phylogeographical studies involving co-distributed animal and plant species have been conducted for several areas, most notably for Europe and the Pacific Northwest of North America. Until recently, phylogeographical studies in unglaciated eastern North America have been largely limited to animals. As more studies emerge for diverse lineages (including plants), it seems timely to assess the phylogeography across this region: (i) comparing and contrasting the patterns seen in plants and animals; (ii) assessing the extent of pseudocongruence; and (iii) discussing the potential applications of regional phylogeography to issues in ecology, such as response to climatic change. Unglaciated eastern North America is a large, geologically and topographically complex area with the species examined having diverse distributions. Nonetheless, some recurrent patterns emerge: (i) maritime - Atlantic vs. Gulf Coast; (ii) Apalachicola River discontinuity; (iii) Tombigbee River discontinuity; (iv) the Appalachian Mountain discontinuity; (v) the Mississippi River discontinuity; and (vi) the Apalachicola River and Mississippi River discontinuities. Although initially documented in animals, most of these patterns are also apparent in plants, providing support for phylogeographical generalizations. These patterns may generally be attributable to isolation and differentiation during Pleistocene glaciation, but in some cases may be older (Pliocene). Molecular studies sometimes agree with longstanding hypotheses of glacial refugia, but also suggest additional possible refugia, such as the southern Appalachian Mountains and areas close to the Laurentide Ice Sheet. Many species exhibit distinct patterns that reflect the unique, rather than the shared, aspects of species' phylogeographical histories. Furthermore, similar modern phylogeographical patterns can result from different underlying causal factors operating at different times (i.e. pseudocongruence). One underemphasized component of pseudocongruence may result from the efforts of researchers to categorize patterns visually - similar patterns may, in fact, not fully coincide, and inferring agreement may obscure the actual patterns and lead to erroneous conclusions. Our modelling analyses indicate no clear spatial patterning and support the hypothesis that phylogeographical structure in diverse temperate taxa is complex and was not shaped by just a few barriers.

Animals↗
PubMed2006

Adherence to antiretroviral therapy in sub-Saharan Africa and North America: a meta-analysis.

CONTEXT: Adherence to antiretroviral therapy is a powerful predictor of survival for individuals living with human immunodeficiency virus (HIV) and AIDS. Concerns about incomplete adherence among patients living in poverty have been an important consideration in expanding the access to antiretroviral therapy in sub-Saharan Africa. OBJECTIVE: To evaluate estimates of antiretroviral therapy adherence in sub-Saharan Africa and North America. DATA SOURCES: Eleven electronic databases were searched along with major conference abstract databases (inclusion dates: inception of database up until April 18, 2006) for all English-language articles and abstracts; and researchers and treatment advocacy groups were contacted. Study Selection and Data Abstraction To best reflect the general population, studies of mixed populations in both North America and Africa were selected. Studies evaluating specific populations such as men only, homeless individuals, or drug users, were excluded. The data were abstracted in duplicate on study adherence outcomes, thresholds used to determine adherence, and characteristics of the populations. A random-effects meta-analysis was performed in which heterogeneity was examined using multivariable random-effects logistic regression. A sensitivity analysis was performed using Bayesian methods. DATA SYNTHESIS: Thirty-one studies from North America (28 full-text articles and 3 abstracts) and 27 studies (9 full-text articles and 18 abstracts) from sub-Saharan Africa were included. African studies represented 12 sub-Saharan countries. Of the North American studies, 71% used patient self-report to assess adherence; this was true of 66% of the African assessments. Studies reported similar thresholds for adherence monitoring (eg, 100%, >95%, >90%, >80%). A pooled analysis of the North American studies (17,573 patients total) indicated a pooled estimate of 55% (95% confidence interval, 49%-62%; I2, 98.6%) of the populations achieving adequate levels of adherence. Our pooled analysis of African studies (12,116 patients total) indicated a pooled estimate of 77% (95% confidence interval, 68%-85%; I2, 98.4%). Study continent, adherence thresholds, and study quality were significant predictors of heterogeneity. Bayesian analysis was used as an alternative statistical method for combining adherence rates and provided similar findings. CONCLUSION: Our findings indicate that favorable levels of adherence, much of which was assessed via patient self-report, can be achieved in sub-Saharan African settings and that adherence remains a concern in North America.

Africa South of the Sahara↗
PubMed2002

The epidemiology of irritable bowel syndrome in North America: a systematic review.

OBJECTIVE: The aim of this study was to systematically review published literature about the prevalence, incidence, and natural history of irritable bowel syndrome (IBS) in North America. METHODS: A computer-assisted search of MEDLINE, EMBASE, and Current Contents/Science Edition databases was performed independently by two investigators. Study selection criteria included: 1) North American population-based sample of adults; 2) objective diagnostic criteria for IBS (i.e., Rome or Manning criteria); and 3) publication in full manuscript form in English. Eligible articles were reviewed in a duplicate and independent manner. Data extracted were converted into individual tables and presented in descriptive form. RESULTS: The prevalence of IBS in North America ranges from 3% to 20%, with most prevalence estimates ranging from 10% to 15%. The prevalences of diarrhea-predominant and constipation-predominant IBS are both approximately 5%. Published prevalence estimates by gender range from 2:1 female predominance to a ratio of 1:1. Constipation-predominant IBS is more common in female individuals. The prevalence of IBS varies minimally with age. No true population-based incidence studies or natural history studies were found. In one cohort surveyed on two occasions 1 yr apart, 9% of subjects who were free of IBS at baseline reported IBS at follow-up producing an onset rate of 67 per 1000 person-years. In all, 38% of patients meeting criteria for IBS did not meet IBS criteria at 1-yr follow-up. CONCLUSION: Approximately 30 million people in North America meet the diagnostic criteria for IBS. However, data about the natural history of IBS is quite sparse and renewed efforts should be focused at developing appropriately designed trials of the epidemiology of IBS.

Age Distribution↗