Compared to what? Finding controls for case-control studies

Fibrinolysis in patients with an abdominal aortic aneurysm with special emphasis on rupture and shock

BACKGROUND

A ruptured abdominal aortic aneurysm (AAA) is associated with high mortality. Postoperative complications such as hemorrhage, multiple organ failure, myocardial infarction, and thromboembolism are common. An active and balanced hemostatic system is essential to avoid bleeding as well as thrombosis. When these activities are not properly regulated the patient is at risk of developing either excessive bleeding or thrombosis-related complications. Previous studies have shown a state of activated coagulation in patients with ruptured AAA. However, there are conflicting results regarding the fibrinolytic response.

OBJECTIVES

The aim of the present study was to investigate the fibrinolytic state pre-operatively in patients with ruptured and non-ruptured AAA in relation to the clinical outcome with special regard to the influence of shock.

METHODS

A prospective study was performed on 95 patients who underwent surgery for a ruptured AAA with shock (n = 43), a ruptured AAA without shock (n = 12), and a non-ruptured AAA (n = 40). Forty-one controls without an aneurysm were matched to the AAA patients according to age, gender and smoking habits. Plasma levels of tissue plasminogen activator antigen (tPAag), and plasminogen activator inhibitor type-1 (PAI-1) were measured as markers of fibrinolytic activity. D-dimer, a marker of fibrin turnover, was also measured.

RESULTS

D-dimer was significantly higher in patients with a non-ruptured AAA compared with controls without AAA. There were significantly higher levels of D-dimer, tPAag, and PAI-1 in patients operated for ruptured compared with non-ruptured AAA. tPAag was also significantly higher in ruptured AAA patients with shock compared with without shock. No deaths occurred in patients operated on for a non-ruptured AAA or ruptured AAA without shock. There were 12 deaths after repair of a ruptured AAA with shock, of which two patients died from bleeding and the remaining 10 from multiple organ failure and cardiac failure.

CONCLUSION

Our results indicate a state of activated coagulation in patients with a non-ruptured AAA, the state being intensified by rupture. The present data show normal fibrinolytic activities in patients with a non-ruptured AAA, but increased systemic fibrinolysis, as demonstrated by elevated tPAag level, in patients with a ruptured AAA. The elevated PAI-1 level indicates a simultaneous inhibition of the systemic fibrinolysis. Furthermore, the hyperfibrinolytic state was reinforced by shock in this study. However, the clinical outcome, with a relatively high incidence of thrombosis-related deaths, indicate a prothrombotic state instead of a hyperfibrinolytic state as a major point of attention in patients with shock as a result of a ruptured AAA.

Lack of association between Chlamydophila pneumoniae seropositivity and abdominal aortic aneurysm

Chronic Chlamydophila pneumoniae infection has been suggested as a possible contributing factor for the development and expansion of abdominal aortic aneurysm (AAA). The relevance of C pneumoniae involved in the processes underlying aneurysmal rupture is unknown. The aim of this study was to examine the relationship between C pneumoniae seropositivity and AAA rupture. In a case-control study, 119 patients with AAA and 36 matched controls were prospectively investigated with C pneumoniae serology. Patients with ruptured AAA have similar levels of IgG antibodies against C pneumoniae as patients with an electively operated AAA, a small AAA, and controls. In conclusion, this study fails to demonstrate a connection between C pneumoniae seropositivity and AAA rupture.

Increased gallstone risk in humans conferred by common variant of hepatic ATP-binding cassette transporter for cholesterol

Genomewide scans of inbred strains of mice have linked the genes encoding the hepatocanalicular cholesterol transporter ABCG5/G8 to gallstone formation. Five nonsynonymous coding single-nucleotide polymorphisms (SNPs) in the orthologous human genes are associated with differences in serum cholesterol and plant sterol levels. We now tested these ABCG5/G8 SNPs for linkage and association with gallstone susceptibility in humans. Prospectively, we collected data from 178 white individuals with gallbladder stones or history of cholecystectomy in 84 families and from 70 stone-free controls, as confirmed by abdominal ultrasound. We performed nonparametric linkage (NPL) analysis of affected sib pairs (ASPs) and association tests of cases and controls. In ASPs, gallstones were strongly linked to the D19H variant of the ABCG8 gene (NPL score = 7.1; P = 4.6 x 10(-13)). The risk of gallstones in carriers of the 19H allele was significantly increased in randomly selected cases from the ASP cohort compared to the stone-free controls (OR = 3.018; P = 0.017). Consistent with the mouse model, heterozygosity for the lithogenic ABCG8 allele was associated with gallstones in humans; 21.4% of gallstone patients carried the heterozygous D19H genotype, compared with 8.6% of controls (OR = 2.954; P = 0.026).

CONCLUSION

The linkage and association studies identified the cholesterol transporter ABCG5/G8 as a genetic determinant of gallstone formation, or LITH gene, in humans. The function of this transporter and the results of the genetic study taken together indicate that in gallstone-susceptible carriers of the ABCG8 19H allele, cholesterol cholelithiasis is secondary to increased hepatobiliary cholesterol secretion.

Selection bias: neighbourhood controls and controls selected from those presenting to a Health Unit in a case control study of efficacy of BCG revaccination

Background

In most case control studies the hardest decision is the choice of the control group, as in the ideal control group the proportion exposed is the same as in the population that produced the cases.

Methods

A comparison of two control groups in a case control study of the efficacy of BCG revaccination. One group was selected from subjects presenting to the heath unit the case attended for routine prevention and care; the second group was selected from the neighbourhood of cases. All Health Units from which controls were selected offered BCG revaccination. Efficacy estimated in a randomized control trial of BCG revaccination was used to establish that the neighbourhood control group was the one that gave unbiased results.

Results

The proportion of controls with scars indicating BCG revaccination was higher among the control group selected from Health Unit attenders than among neighbourhood controls. This excess was not removed after control for social variables and history of exposure to tuberculosis, and appears to have resulted from the fact that people attending the Health Unit were more likely to have been revaccinated than neighbourhood controls, although we can not exclude an effect of other unmeasured variables.

Conclusion

In this study, controls selected from people presenting to a Health Unit overrepresented exposure to BCG revaccination. Had the results from the HU attenders control group been accepted this would have resulted in overestimation of vaccine efficacy. When the exposure of interest is offered in a health facility, selection of controls from attenders at the facility may result in over representation of exposure in controls and selection bias.

Multiple-drug-resistant bacteria in patients with severe acute exacerbation of chronic obstructive pulmonary disease: Prevalence, risk factors, and outcome

OBJECTIVE

To determine prevalence, risk factors, and effect on outcome of multiple-drug-resistant (MDR) bacteria in patients with severe acute exacerbation of chronic obstructive pulmonary disease.

DESIGN

Prospective, observational, cohort study.

SETTING

Thirty-bed medical intensive care unit (ICU) in a university hospital.

METHODS

All chronic obstructive pulmonary disease patients with acute exacerbation who required intubation and mechanical ventilation for >48 hrs were eligible during a 4-yr period. Patients with pneumonia or other causes of acute respiratory failure were not eligible. In all patients, quantitative tracheal aspirate was performed at ICU admission (positive at 10 colony-forming units [cfu]/mL). MDR bacteria were defined as methicillin-resistant Staphylococcus aureus, ceftazidime- or imipenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and extended-spectrum beta-lactamase-producing Gram-negative bacilli. All patients received empirical antibiotic treatment at ICU admission. Univariate and multivariate analyses were used to determine variables associated with MDR bacteria and variables associated with ICU mortality.

RESULTS

A total of 857 patients were included, and 304 bacteria were isolated (>/=10 cfu/mL) in 260 patients (30%), including 75 MDR bacteria (24%) in 69 patients (8%). When patients with MDR bacteria were compared with patients without MDR bacteria, previous antimicrobial treatment (odds ratio [OR], 2.4; 95% confidence interval [95% CI], 1.2-4.7; p = .013) and previous intubation (OR, 31; 95% CI, 12-82; p < .001) were independently associated with MDR bacteria. When patients with bacteria other than MDR or patients with no bacteria were used as a reference group, these risk factors were still independently associated with MDR bacteria. Although ICU mortality rate was higher in patients with MDR bacteria than in patients without MDR bacteria (44% vs. 25%; p = .001; OR, 2.3; 95% CI, 1.4-3.8), MDR bacteria were not independently associated with ICU mortality. Inappropriate initial antibiotic treatment (88% vs. 5%; p = <.001; OR, 6.7; 95% CI, 3.8-12) and ventilator-associated pneumonia (23% vs. 5%; p = <.001; OR, 1.3; 95% CI, 1-1.8) rates were significantly higher in patients with MDR bacteria than in patients with bacteria other than MDR. Inappropriate initial antibiotic treatment was independently associated with increased ICU mortality (OR, 7.1; 95% CI, 1.9-30; p = .003).

CONCLUSION

MDR bacteria are common in patients with acute exacerbation of chronic obstructive pulmonary disease requiring intubation and mechanical ventilation. Previous antimicrobial treatment and previous intubation are independent risk factors for MDR bacteria. Although MDR bacteria are not independently associated with ICU mortality, inappropriate initial antibiotic treatment is an independent risk factor for ICU mortality in these patients. Further studies are needed to determine whether broad-spectrum antibiotic treatment is cost-effective in these patients.

Test characteristics of placental location screening by transabdominal ultrasound at 18-20 weeks

OBJECTIVES

To determine the test characteristics of a second-trimester transabdominal fetal anomaly scan in screening for placenta previa.

PATIENTS AND METHODS

This was a case-control study carried out at a tertiary obstetric hospital involving 54 women (0.5% of the total number booked for antenatal care and delivery at the center) with clinically significant placenta previa at the time of delivery, and 168 randomly selected controls who attended for antenatal care and delivery in 2000-2003. Sensitivity, specificity and false positive rate of the placenta-os measurement in the second-trimester transabdominal fetal anomaly scan for identification of clinically significant placenta previa were assessed.

RESULTS

Women with placenta previa at delivery had significantly different second-trimester placenta-os measurements from those of controls (P < 0.0001). For women with placenta previa, the mean (standard deviation) placenta-os measurement was -0.96 cm (1.95) vs. 4.15 cm (1.77) for controls (P < 0.0001). Using the anomaly scan as a screening test for placenta previa with a placenta-os measurement cut-off point of < or = 2 cm, all cases of placenta previa should be identified, but 11.1% (95% CI, 7.1-14.8) of women without placenta previa would have false positive results. At cut-off points of 3 cm and 1.5 cm the false positive rates were 25.7% (95% CI, 18.8-30.2%) and 6.6% (95% CI, 3.8-9.6%), respectively, but at 1.5 cm 3.8% of cases would be missed.

CONCLUSIONS

The second-trimester transabdominal fetal anomaly scan is a useful screening test for placenta previa. However, because of false positives among the much larger population of women without placenta previa, we estimate that with a cut-off point of < or =2 cm, 23 women would have to be followed up to confirm one true placenta previa.

Economic causes and effects of AIDS in South African households

OBJECTIVE

To investigate the magnitude and temporal directionality of associations between illness and death, and income and expenditure, in households affected by HIV/AIDS.

DESIGN AND SUBJECTS

A cohort study with repeated measures carried out in 405 households (1913 occupants), known to have HIV-infected occupants and their neighbours, in one rural and one urban area of South Africa.

MAIN OUTCOME MEASURES

Monthly adult equivalent income and expenditure. Illness episodes and deaths attributed to HIV/AIDS, tuberculosis and pneumonia.

METHODS

Interview surveys of household heads were conducted at baseline and five more times, biannually, providing information on household economics, illnesses and deaths. Regression analyses used marginal structural models and 'before-after' models to analyse changes.

RESULTS

In marginal structural models, current or previous AIDS illness was independently associated with 34% [95% confidence intervals (CI) 23-43%] lower monthly expenditure, and current or recent poverty was associated with 1.74 (95% CI 0.94-3.2) times higher odds of an AIDS death. In before-after models, each AIDS death was independently associated with a 23% (95% CI 11-34%) greater expenditure decline over 3 years, and a 100 US dollars higher monthly expenditure at baseline was associated with 0.31 (95% CI 0.13-0.74) times as many AIDS deaths and with 0.41 (95% CI 0.27-0.64) times as many AIDS illness episodes over 3 years.

CONCLUSION

AIDS deaths and illnesses predicted declining expenditure and poverty predicted AIDS, suggesting that both welfare and effective treatment are needed.

Quality of life is decreased after treatment for nonfunctioning pituitary macroadenoma

OBJECTIVE

Although a reduced quality of life (QoL) has been reported after long-term cure of functioning pituitary adenomas, the effect of successful treatment of nonfunctioning pituitary macroadenoma (NFMA) on QoL has not been fully addressed. Therefore, we evaluated a broad spectrum of QoL parameters in patients successfully treated for NFMA in our center.

DESIGN

We conducted a case-control study.

PATIENTS AND METHODS

We assessed QoL in 99 adult patients (mean age, 61.9 yr; range, 24-86 yr) in remission during long-term follow-up after surgical (n = 99) and additional radiotherapeutic (n = 37) treatment for NFMA by four validated health-related questionnaires (Hospital Anxiety and Depression Scale, Multidimensional Fatigue Index, Nottingham Health Profile, and Short Form-36). Patient outcomes were compared with 125 controls and with age-adjusted reference values derived from the literature.

RESULTS

NFMA patients reported significantly impaired QoL in all questionnaires compared with the 125 controls and the age-adjusted reference values. All subscales of fatigue, assessed using the Multidimensional Fatigue Index (general fatigue, physical fatigue, reduction in activity, reduction in motivation, and mental fatigue) were impaired. The scores in the Nottingham Health Profile pointed toward reduced energy and affected emotional reaction. In several subscales of the Short Form-36 (social functioning, role limitations due to physical problems, role limitations due to emotional problems, and general health perception), NFMA patients reported a reduced QoL.

CONCLUSION

QoL is considerably reduced in patients after successful treatment of NFMA.

Risk of Lung Cancer and Exposure to Industrial Acids, Solvents, and Metals in Leningrad Province, Russia

OBJECTIVE

We sought to investigate the association of occupational exposure to industrial acids, solvents, and metals with lung cancer in Leningrad Province, Russia, where an excess of occupationally related lung cancer was reported recently.

METHODS

We identified 540 pathologically diagnosed lung cancer cases and 582 controls from the 1993-1998 autopsy records of the 88 Leningrad Province hospitals. Lifetime job-specific exposure measurements were available for 12 industrial acids, 15 solvents, and 17 metals.

RESULTS

Exposures were frequent in the study group and mostly occurred after World War II. However, lung cancer risks for industrial acids (odds ratio [OR] = 1.2; 95% confidence interval [CI] = 0.8-1.7), solvents (OR = 0.8; 95% CI = 0.6-1.2), and metals (OR = 0.8; 95% CI = 0.5-1.0) were not increased. Also, no significant excess risk was found for any of the specific agents investigated.

CONCLUSIONS

The excess of occupationally related lung cancer in the Province is not explained by exposure to the agents investigated.