Case-control Investigations Research Articles

Polychlorinated biphenyls (PCB), UV radiation, and cutaneous malignant melanoma

Several older epidemiologic studies have suggested that exposure to polychlorinated biphenyls (PCBs) may increase risk of cutaneous malignant melanoma (CMM). These investigations, however, have not been able to control for sun exposure, and sun sensitivity, which are major risk factors for this cancer. We conducted a pilot study to examine the possible association between plasma levels of PCBs and risk of CMM, controlling for sun exposure and sun sensitivity. Our case-control study compared levels of 14 PCB congeners in the plasma of 80 Caucasian CMM patients, and 310 Caucasian controls frequency matched by age group and gender. Assays were conducted using gas chromatography and values were lipid-adjusted. Data concerning sun exposure history, sun sensitivity, and host pigmentation variables such as skin, eye and hair colour were also collected using standardized questionnaires. Odds ratios and 95% confidence intervals were calculated for total PCBs, dioxin-like and non-dioxin like PCBs, as well as individual congeners using unconditional logistic regression. A strong association was seen between melanoma risk and plasma levels of total PCBs, (OR highest quartile: 6.02; 95% CI = 2.00-18.17); non-dioxin-like PCBs (OR highest quartile:7.02; 95%CI = 2.30-21.43); and many of the single congeners. These associations persisted after adjustment for recreational sun exposure, sun sensitivity and pigmentation factors. Although the study results will require independent confirmation in larger case-control or cohort investigations, they suggest that potential environmental factors other than UV radiation may be involved in melanoma.

WUPyV in Children with Acute Respiratory Tract Infections, China

WUPyV in Children with Acute Respiratory Tract Infections, China

Confirmation of the novel association at the BTNL2 locus with ulcerative colitis

Linkage in families and association in population case-control investigations have clearly shown that genes within the major histocompatibility complex region on chromosome 6p are relevant to the susceptibility and pathogenesis of ulcerative colitis (UC) and Crohn's disease. However, identifying the causative variants by fine mapping has not been conclusive. In this study using 58 single nucleotide polymorphisms (SNPs) with 616 UC cases, there was significant association with SNP rs2294881 of the (butyrophilin-like 2) BTNL2 gene with odds ratio (OR) = 2.80, confidence interval (CI) = 1.62-4.84 and P = 5.69 x 10(-4) (P(Bonferroni) = 3.3 x 10(-2)) and replication of SNP rs9268480. The missense SNP rs2076523 (K196E) showed novel association with a subset of UC cases with colectomy (n = 126), OR = 0.25, CI = 0.11-0.58 and P = 4.42 x 10(-4) (P(Bonferroni) = 2.56 x 10(-2)). These three associated variants within the BTNL2 gene were neither in linkage disequilibrium with each other nor correlated with the SNPs tagging the human leukocyte antigen (HLA)-DRB1*1502 and HLA-DRB1*0301 alleles.

Triple X syndrome in a patient with partial lipodystrophy discovered using a high-density oligonucleotide microarray: a case report

IntroductionPatients with lipodystrophy experience selective or generalized atrophy of adipose tissue. The disruption of lipid metabolism results in an increased risk for development of metabolic syndrome and coronary artery disease. Currently, the mutations responsible for approximately half of lipodystrophy patients are known, but new techniques and examination of different types of genetic variation may identify new disease-causing mechanisms.Case presentationA 53-year-old woman of African descent was referred to a tertiary care endocrinology clinic for treatment of severe insulin resistance, treatment-resistant hypertension and dyslipidemia. After all known lipodystrophy-causing mutations were excluded by DNA sequencing, the patient was found to have triple X syndrome after an initial investigation into copy number variation using a high-density oligonucleotide microarray. The patient also had a previously unobserved duplication of 415 kilobases of chromosome 5q33.2. This is the first case report of a patient with lipodystrophy who also had triple X syndrome.ConclusionWhile we cannot make a direct link between the presence of triple X syndrome and partial lipodystrophy, if unrelated, this is an extremely rare convergence of syndromes. This patient poses an interesting possibility regarding the influence triple X syndrome may have on an individual with other underlying lipodystrophy susceptibility. Finally, impending large-scale case-control and cohort copy number variation investigations will, as a by-product, further document the prevalence of triple X syndrome in various patient groups.

Physical activity and premenopausal breast cancer: an examination of recall and selection bias

Compared with cohort studies, case-control investigations have tended to report clearer protective associations for the relationship between physical activity and premenopausal breast cancer risk. We conducted a case-control study within the Nurses' Health Study II cohort to examine whether recall or selection bias could explain the stronger protective associations. Self-reported total recreational physical activity during adulthood and over a woman's lifetime (ages 12 years to current) were assessed in 1997 before diagnosis and, again, from one to seven years after breast cancer diagnosis among the same women. Eighty-seven percent of cases (417 of 479) and 82% of controls (390 of 474) responded. Selection bias was observed for activity during adulthood but not for activity over a woman's lifetime. Recall bias was not observed in the direction we expected: the odds ratios (ORs) for breast cancer comparing the highest versus lowest quintile of prospectively reported total activity were not significantly different than the corresponding estimates from retrospective reports (e.g., lifetime activity: prospective OR = 0.58, 95% CI: 0.37, 0.93 versus retrospective OR = 0.80; 95% CI: 0.50, 1.29). Recall or selection bias may not have been accounted for protective associations among case-control investigations examining lifetime recreational physical activity and breast cancer. Selection bias related to recreational physical activity during adulthood and random error in the measurement of physical activity remain concerns.

Problems occurring in the application of cytogenetic biomarkers for alcoholics with and without malignant diseases

Applicability of alcohol- and smoking-related cancer-risk biomarkers might be modified by several factors. Among those, reality of self-reports on alcohol consumption of alcoholic patients with different diseases and extreme high mutagen hypersensitivity of Hungarians, as well as the immunologic role of peripheral lymphocytes as experimental objects of cytogenetic biomarkers seem to be new viewpoints of interest. To clarify these problems, 432 head and neck cancer patients (HNCP), 62 alcoholics with alcoholic hepatitis (ALCL), and 101 disease-free chronic alcoholics (ALC) were examined. Despite clinically confirmed alcohol-related diagnoses (and GGT and MCV values) only about half of HNCPs and ALCLs reported about any alcohol consumption, in contrast to the realistic self-reports of ALCs. In cytogenetic case control investigations no difference between the spontaneous rate of chromosomal aberrations (CAs) of healthy controls and ALCs was found, however, genetic instability expressed as a 40-50% elevation rate of CAs in HNCPs and ALCLs might be associated with systemic inflammatory reaction of lymphocytes. Bleomycin sensitivity assay showed the highest break/cell (b/c) values not in HNCPs (1.06 b/c) as it was reported earlier, but in "healthy" ALCs (1.52 b/c). This phenomenon can be related to the local effect of genotoxins (alcohol, smoking, and in particular the diet), which probably reflects merely a reaction of mucosal immune system. Nearly 50% of mutagen-hypersensitive Hungarian controls, in contrary to the expected 10-20% ones, might also be explained by this. Similarly, HNCPs with oral cancer, where the local mutagen effect was the most intensive, had the highest b/c values. In conclusion, when cytogenetic biomarkers of alcoholism are examined, the subjective character of self-reports at epidemiologic level and immunologic role of lymphocyte subpopulations as genetic confounders must also be taken into consideration.

Prevalence and molecular characterization of WU/KI polyomaviruses isolated from pediatric patients with respiratory disease in Thailand

WU and KI polyomaviruses represent novel viruses discovered in respiratory secretions from human patients with acute respiratory tract infection. However, the association between WU/KI polyomaviruses and human disease has remained unclear. In this study, the prevalence of these two novel viruses and occurrence of co-infection with other respiratory viruses were determined in Thai pediatric patients with respiratory disease. Previously described PCR assays were applied to detect WU/KI polyomaviruses as well as other respiratory viruses in 302 nasopharyngeal suction specimens collected from February 2006 through February 2007. The results revealed the anneal prevalence of WU and KI polyomaviruses in the Thai population was 6.29% and 1.99%, respectively. The frequency of co-detection of WU and KI polyomaviruses with other respiratory viral pathogens was 42.11% and 33.33%, respectively. Moreover, each of the two complete genome sequences of WU (CU_295 and CU_302) and KI (CU_255 and CU_258) polyomaviruses were genetically and phylogenetically characterized. Sequence analysis showed that they contained features common to those found in previous studies. However, there were several nucleotide variations within the non-coding regulatory regions and various non-synonymous mutations within the coding regions which may influence virulence and pathogenesis of these viruses. Nevertheless, it is still possible that these viruses are not the causative agents of clinical respiratory disease. Therefore, judging the association of WU/KI polyomavirus infections with a particular disease will be challenging and require more comprehensive case control investigations.

Prophylaxis of Infective Endocarditis: Prevention of the Perfect Storm

Despite the availability of endocarditis prophylaxis guidelines for more than five decades, no prospective, randomised trial has ever been conducted to evaluate the efficacy and safety of this practice. This fact, in combination with mixed results from case-control investigations and other factors, has prompted a re-evaluation of the appropriateness of the guidelines. The update provided herein highlights recent revisions in guidelines promulgated by different countries.

Editor’s Choice

Editor’s Choice

Overview of hemostatic factors involved in atherosclerotic cardiovascular disease

Hemostatic factors associated with the development of cardiovascular disease (CVD) include fibrinogen, von Willebrand factor, tissue plasminogen activator (tPA) antigen, plasminogen activator inhibitor-1 (PAI-1), and factor VII. Each SD increment of these increases the association by 24-30%. Most hemostatic factors are intercorrelated with inflammatory markers [e.g., C-reactive protein (CRP)] and LDL cholesterol. Fibrinogen seems the most fundamental hemostatic risk factor for CVD. The Framingham Study reaffirms the significant linear risk factor trends across fibrinogen tertiles (P< 0.001) for age, body mass index, smoking, diabetes mellitus, total cholesterol, HDL cholesterol, and TG in both sexes. Fibrinogen may also directly increase CVD risk because of its role in platelet aggregation, plasma viscosity, and fibrin formation. Fibrinogen is also an acute-phase reactant that is elevated in inflammatory states. Fibrinogen mediates the thrombogenic effect of other risk factors. Fibrinogen levels increase with the number of cigarettes smoked and quickly fall after smoking cessation. This rapid fibrinogen decline may be a mechanism for CVD risk reduction after smoking cessation. Weight loss is accompanied by reduced fibrinogen. The correlation between fibrinogen and LDL cholesterol suggests that lipid-imposed CVD risk is mediated partly through fibrinogen. Hyperreactive platelets of diabetics may result in part from their increased fibrinogen. Elevated fibrinogen and CRP of unstable angina suggest an acute-phase reaction. Prevalence, case-control, angiographic, and echocardiogram investigations incriminate hemostatic and inflammatory markers as strong independent risk factors for initial and recurrent CVD. Framingham Study data indicate that each SD increase in fibrinogen imposes a 20% independent increment in risk. It may be concluded that fibrinogen and CRP determination may be useful screening tools to identify individuals at added risk for thrombotic complications of CVD.

Suicide and Attempted Suicide in Bipolar Disorder

To determine the main risk factors for suicide and nonfatal suicidal behavior in patients with bipolar disorder through a systematic review of the international literature. Studies were identified through electronic searches of MEDLINE (1966-December 2003), EMBASE (1980-December 2003), PsycINFO (1872-November 2003), and Biological Abstracts (1985-December 2003) using index and free-text search terms for bipolar disorder, bipolar depression, manic depression, mania, and affective disorders; combined with terms for self-harm, self-injury, suicide, attempted suicide, automutilation, self-mutilation, self-poisoning, and self-cutting; and combined with terms for risk, case control, cohort, comparative, longitudinal, and follow-up studies. No language restrictions were applied to the search. Included studies were cohort, case-control, and cross-sectional investigations of patients with bipolar disorder in which suicide (13 studies) or attempted suicide (23 studies) was reported as an outcome. The selected studies also used diagnostic tools including the DSM, International Classification of Diseases, and Research Diagnostic Criteria. Meta-analysis of factors reported in more than 1 study identified the main risk factors for suicide as a previous suicide attempt and hopelessness. The main risk factors for nonfatal suicidal behavior included family history of suicide, early onset of bipolar disorder, extent of depressive symptoms, increasing severity of affective episodes, the presence of mixed affective states, rapid cycling, comorbid Axis I disorders, and abuse of alcohol or drugs. Prevention of suicidal behavior in patients with bipolar disorder should include attention to these risk factors in assessment and treatment, including when deciding whether to initiate treatment aimed specifically at reducing suicide risk.

Retrospective review of 208 patients with leiomyosarcoma of the uterus: prognostic indicators, surgical management, and adjuvant therapy☆

Objective We evaluated the predictive value of several proposed prognostic indicators and the effect of surgical management and adjuvant therapy on clinical outcome associated with leiomyosarcoma (LMS) of the uterus. Methods A medical record search of patients treated at Mayo Clinic from 1976 through 1999 was performed using the International Classification of Diseases, Ninth Revision codes for LMS and malignant neoplasm of the uterus. Study inclusion criteria included confirmation of the diagnosis of LMS of the uterus by a pathologist at our institution. Survival curves were generated using the Kaplan–Meier method. Multivariate analysis was performed using the Cox proportional hazards model. A case-control investigation was also performed. Results A total of 208 patients met study requirements. The median follow-up for survivors was 7.7 years. Multivariate analysis showed that high grade, advanced stage, and oophorectomy were associated with significantly worse disease-specific survival. Case-control investigations suggested that ovarian preservation does not adversely affect survival and that adjuvant pelvic radiation therapy does not significantly improve survival. An LMS risk-assessment index that was generated is highly predictive of survival. Conclusions Tumor grade and stage (using modified criteria for endometrial cancer) appear to be valid prognostic indicators for LMS of the uterus. Ovarian preservation may be considered in premenopausal patients with early-stage leiomyosarcoma of the uterus. Additionally, adjuvant therapy does not appear to significantly affect survival. Finally, our highly predictive LMS risk-assessment index may be useful for counseling patients.

Sexual behavior and evidence for an infectious cause of prostate cancer.

The association of geographic/racial heterogeneity of prostate cancer rates with the effects of migration has been interpreted as evidence of the impact of environmental factors on the risk of prostate tumorigenesis. A number of epidemiologic studies have supported the hypothesis that ethnic differences observed in prostate cancer rates are attributed to cultural variations in male sexual behavior. Several case-control investigations have also suggested the association of prostate cancer with sexual history particularly the history of sexually transmitted disease but such relations have not been firmly established. Furthermore virologic studies have initially focused on herpes viruses since it was thought that such agents play a major role in cervical cancer. Although the herpes viruses are human cancer viruses there is little evidence on the effect of herpes viruses on the risk of prostate cancer. In this regard researches have focused on the etiologic role of human papillomavirus (HPV) in prostate cancer. However inconsistency of HPV detection in prostate cancer cells is noted due to failure of studies using sensitive polymerase chain reaction assays in contrast to its marked association with cervical cancer. In this regard the search for an infectious etiology of prostate cancer would require a special commitment by researchers epidemiologists and clinicians to overcome high costs and risks of failures.

Obstetric Risk Factors for Early-Onset Schizophrenia in a Finnish Birth Cohort

Although case-control investigations have shown an association between obstetric complications and schizophrenia, particularly among patients with early onsets, cohort studies have mostly failed to confirm this effect. The authors examined whether a history of fetal hypoxia and other obstetric complications elevated risk for early-onset schizophrenia in a 1955 Helsinki birth cohort. The subjects were 80 randomly selected patients with schizophrenia (36 with early and 44 with later onsets) representative of all available probands in the cohort, 61 of their nonschizophrenic siblings, and 56 demographically matched nonpsychiatric comparison subjects. Psychiatric diagnoses were obtained from structured clinical interviews, and obstetric data were taken from standardized, prospectively ascertained obstetric records. A score for hypoxia-associated obstetric complications was entered into logistic regression models, along with measures of prenatal infection and fetal growth retardation. Hypoxia-associated obstetric complications significantly increased the odds of early-onset schizophrenia but not of later-onset schizophrenia or unaffected sibling status, after prenatal infection and fetal growth retardation were taken into account. These findings support an association between obstetric complications and increased risk for early-onset schizophrenia. The authors advance a model whereby the neurotoxic effects of fetal hypoxia may lead to an early onset of schizophrenia due to premature cortical synaptic pruning.

Investigation of multidrug-resistant Salmonella serotype typhimurium DT104 infections linked to raw-milk cheese in Washington State.

Multidrug-resistant Salmonella Typhimurium DT104 has recently emerged as a cause of human and animal illness in Europe and North America. In early 1997, health officials in Yakima County, Washington, noted a 5-fold increase in salmonellosis among the county's Hispanic population. To characterize bacterial strains and identify risk factors for infection with Salmonella Typhimurium in Yakima County. Laboratory, case-control, and environmental investigations. Patients with culture-confirmed Salmonella Typhimurium infection living in Yakima County and age- and neighborhood-matched control subjects. Food vehicle implication based on case-control study and outbreak control. Between January 1 and May 5, 1997, 54 culture-confirmed cases of Salmonella Typhimurium were reported. The median age of patients was 4 years and 91% were Hispanic. Patients reported diarrhea (100%), abdominal cramps (93%), fever (93%), bloody stools (72%), and vomiting (53%); 5 patients (9%) were hospitalized. Twenty-two patients and 61 control subjects were enrolled in the case-control study. Seventeen case patients (77%) reported eating unpasteurized Mexican-style soft cheese in the 7 days before onset of illness compared with 17 control subjects (28%) (matched odds ratio, 32.3; 95% confidence interval, 3.0-874.6). All case-patient isolates were phage definitive type 104 (DT104) (n = 10) or DT104b (n = 12), and 20 (91%) were resistant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline. The cheese produced and eaten by 2 unrelated patients was made with raw milk traced to the same local farm. Milk samples from nearby dairies yielded Salmonella Typhimurium DT104. The incidence of Salmonella Typhimurium infections in Yakima County returned to pre-1992 levels following interventions based on these findings. Multidrug-resistant Salmonella Typhimurium DT104 emerged as a cause of salmonellosis in Yakima County, and Mexican-style soft cheese made with unpasteurized milk is an important vehicle for Salmonella Typhimurium DT104 transmission. We postulate that recent increases in human salmonellosis reflect the emergence of Salmonella Typhimurium DT104 among dairy cows in the region. Continued efforts are needed to discourage consumption of raw milk products, promote healthier alternatives, and study the ecology of multidrug-resistant Salmonella Typhimurium.

Hospitalizations for Aplastic Anemia and Agranulocytosis in Saskatchewan: Incidence and Associations with Antecedent Prescription Drug Use

A population-based study to estimate the incidence of hospitalizations for aplastic anemia and agranulocytosis and to evaluate associations between these disorders and antecedent prescription drug use was performed using the Saskatchewan administrative health care databases. Hospital charts and cancer registration data were utilized to apply strict diagnostic criteria to case identification. Estimates of the annual incidence of aplastic anemia and agranulocytosis were 2.7 and 3.0 per million, which are similar to those from other recent population-based studies with comparable case identification criteria. Only a small number of cases were available to evaluate potential drug causes, leading to an analysis of limited power. Nevertheless, significant associations were found between aplastic anemia and tocainide, gold salts, and antidepressants; and between agranulocytosis and anti-thyroids, trimethoprim-sulfamethoxazole, β-lactams, sulfasalazine, chlorpromazine, carbamazepine, glyburide, and procainamide, although the associations with antibiotics may indicate a response to the disorders rather than a possible cause. These findings are generally consistent with the results of other case-control investigations.

Seroepidemiology ofTrypanosoma cruzi, Etiologic Agent of Chagas' Disease, in US Blood Donors

A comprehensive seroepidemiologic study was conducted in two Red Cross regions (Los Angeles and Miami) to determine the prevalence of Trypanosoma cruzi antibodies in at-risk blood donors, to identify additional risk factors, and to assess the likelihood of transmitting T. cruzi by transfusion. At-risk and control donors were stratified by a broad risk question, tested for T. cruzi antibodies, and if confirmed as seropositive, enrolled in case-control and lookback investigations. A total of 299,398 donors were queried; 23,978 at-risk and 25,587 control donations were tested, and T. cruzi antibodies were confirmed in 34 donors (33 and 1, respectively). Seropositive donors shared one risk factor; birth/extensive time in a T. cruzi-endemic area. Lookback studies identified 11 recipients, all negative for T. cruzi antibodies. Screening strategies that use a question are unlikely to identify all seropositive donors. The lack of definitive data on the risk of transmission by transfusion indicates additional studies of donors and recipients are needed.

A large community outbreak of salmonellosis caused by intentional contamination of restaurant salad bars.

This large outbreak of foodborne disease highlights the challenge of investigating outbreaks caused by intentional contamination and demonstrates the vulnerability of self-service foods to intentional contamination. To investigate a large community outbreak of Salmonella Typhimurium infections. Epidemiologic investigation of patients with Salmonella gastroenteritis and possible exposures in The Dalles, Oregon. Cohort and case-control investigations were conducted among groups of restaurant patrons and employees to identify exposures associated with illness. A community in Oregon. Outbreak period was September and October 1984. A total of 751 persons with Salmonella gastroenteritis associated with eating or working at area restaurants. Most patients were identified through passive surveillance; active surveillance was conducted for selected groups. A case was defined either by clinical criteria or by a stool culture yielding S Typhimurium. The outbreak occurred in 2 waves, September 9 through 18 and September 19 through October 10. Most cases were associated with 10 restaurants, and epidemiologic studies of customers at 4 restaurants and of employees at all 10 restaurants implicated eating from salad bars as the major risk factor for infection. Eight (80%) of 10 affected restaurants compared with only 3 (11%) of the 28 other restaurants in The Dalles operated salad bars (relative risk, 7.5; 95% confidence interval, 2.4-22.7; P<.001). The implicated food items on the salad bars differed from one restaurant to another. The investigation did not identify any water supply, food item, supplier, or distributor common to all affected restaurants, nor were employees exposed to any single common source. In some instances, infected employees may have contributed to the spread of illness by inadvertently contaminating foods. However, no evidence was found linking ill employees to initiation of the outbreak. Errors in food rotation and inadequate refrigeration on ice-chilled salad bars may have facilitated growth of the S Typhimurium but could not have caused the outbreak. A subsequent criminal investigation revealed that members of a religious commune had deliberately contaminated the salad bars. An S Typhimurium strain found in a laboratory at the commune was indistinguishable from the outbreak strain. This outbreak of salmonellosis was caused by intentional contamination of restaurant salad bars by members of a religious commune.

Influence of fibrinogen on cardiovascular disease.

Results from prevalence, case-control, angiographic and echocardiographic investigations incriminate elevated fibrinogen levels as a strong independent risk factor for the occurrence of initial and recurrent cardiovascular events. Average fibrinogen levels are higher in women and persons with other risk factors including hypertension, diabetes, cigarette smoking, obesity, elevated haematocrit value and dyslipidaemia. Fibrinogen tends to cluster with most of these major atherogenic cardiovascular risk factors and further enhances their risk. Prospective data indicate a relationship between fibrinogen and the subsequent development of all the major atherosclerotic cardiovascular events including coronary heart disease, stroke and peripheral artery disease. Fibrinogen adds to the multivariate risk of cardiovascular events, especially in the high risk subset of the population. In the Framingham Heart Study, a comparison of risk gradients, exemplified by their regression coefficients, was similar for all outcomes (coronary heart disease, stroke, peripheral artery disease and cardiovascular disease) in men, whereas, in women, the risk gradient for fibrinogen appeared weakest for stroke. Fibrinogen exerts an independent influence on the frequency of cardiovascular disease in general, and coronary heart disease in particular. For example, in both men and women, each standard deviation increase in fibrinogen level (about 0.56 g/L) within the range of usual values is associated with about a 20% age- and risk factor-adjusted increase in the incidence of an initial cardiovascular event. Fibrinogen should be added to the list of major atherogenic cardiovascular risk factors; in addition, there is a need for intervention trials designed to test the efficacy of lowering fibrinogen in individuals at high risk for cardiovascular disease.

Nosocomial Outbreak Caused by a Multiresistant Clone of Acinetobacter baumannii: Results of the Case-Control and Molecular Epidemiologic Investigations

To describe a nosocomial outbreak caused by multiresistant Acinetobacter baumannii.Descriptive and case-control study. Antibiotic susceptibilities and pulsed-field gel electrophoresis (PFGE) of genomic DNA digested with SfiI and also with ApaI were used as markers of strain identity.A large medical school-affiliated hospital in the city of Houston, Texas.During a 10-week period, A baumannii was isolated from 25 patients admitted to the intensive care unit (ICU). The attack rate was 14.3 per 100 ICU admissions. Case patients were intubated more frequently and for longer periods, and had longer ICU and hospital stays (P < 0.05 for each of these characteristics). Multivariate logistic regression analysis identified the length of ICU stay and the use of third-generation cephalosporins as associated with the acquisition of A baumannii. Patients infected with A baumannii had a higher mortality rate than colonized patients and control patients (P < 0.01). Sixteen isolates recovered from these 25 patients were susceptible only to imipenem/cilastatin, and PFGE confirmed that a single clone was the cause of this outbreak. Nine isolates of A baumannii from patients infected or colonized in two other hospitals in Houston during the same period, differed from the outbreak isolates by their susceptibility to ciprofloxacin. However, PFGE results were identical, indicating unsuscepted genetic relatedness among isolates from three different hospitals.A baumannii is an important nosocomial opportunistic pathogen and can adversely affect the outcome of ICU patients who acquire this organism. This outbreak was caused by a single clone that was isolated concurrently from three hospitals.