Association of influenza vaccination and reduced risk of recurrent myocardial infarction

National availability of influenza vaccine among medical subspecialty practices

BACKGROUND

Influenza vaccination rates fall short of national goals, particularly among individuals whose chronic conditions predispose them to complications of influenza. Availability of influenza vaccine in medical subspecialists' practices may affect vaccination rates among adults with chronic illness.

METHODS

The practice sites of a national random sample of medical cardiology, endocrinology, and pulmonology physicians were contacted by telephone in February 2003 to March 2003 to determine which of them had influenza vaccine available to their patients during the 2002-2003 influenza season. The number of physicians in the practice and geographic location were also obtained.

RESULTS

Office staff at the practices of 1683 of 2013 eligible physicians were successfully contacted, and 1473 provided information about vaccine availability. Overall, 1094 (74%) of practices had influenza vaccine available during the 2002-2003 season. Availability differed significantly by subspecialty: 54% cardiology, 78% endocrinology, and 90% pulmonology (p<0.001). Influenza vaccine was more often available at subspecialists' practices in the Northeast (80%) than in the South (74%), Midwest (71%), and West (70%; p<0.005). In multivariate analyses, pulmonology practices in all census regions and sizes were significantly more likely to have influenza vaccine available than was the reference cardiology practice. Several endocrinology practice types also had significantly higher influenza vaccine availability than those in cardiology practice, particularly in multi-physician practices.

CONCLUSIONS

Influenza vaccine availability varies widely across practices in the three medical subspecialties that provide care to the largest numbers of individuals with an indication for the vaccine in the United States. These findings have implications for the accessibility of influenza vaccine to individuals at high risk for morbidity and mortality associated with influenza.

Viral Community-Acquired Pneumonia in Nonimmunocompromised Adults

INTRODUCTION

Viral community-acquired pneumonia (CAP) has been poorly studied and clinically characterized. Using strict criteria for inclusion, we studied this type of infection in a large series of hospitalized adults with CAP.

MATERIALS AND METHODS

All nonimmunocompromised adult patients with a diagnosis of CAP having paired serology for respiratory viruses (RVs) [338 patients] were prospectively included in the study from 1996 to 2001 at our 1,000-bed university teaching hospital, and subsequently were followed up. We compared patients with pure viral (PV), mixed viral (RV + bacteria), and pneumococcal CAP. RVs (ie, influenza, parainfluenza, respiratory syncytial virus, and adenovirus) were diagnosed by means of paired serology.

RESULTS

Sixty-one of 338 patients (18%) with paired serology had an RV detected, and in 31 cases (9%) it was the only pathogen identified. Influenza was the most frequent virus detected (39 patients; 64%). Patients with chronic heart failure (CHF) had an increased risk of acquiring PV CAP (8 of 26 patients; 31%) when compared to a mixed viral/bacterial etiology (2 of 26 patients; 8%; p = 0.035) or CAP caused by Streptococcus pneumoniae (1 of 44 patients; 2%; p = 0.001). Multivariate analysis revealed that CHF (odds ratio [OR], 15.3; 95% confidence interval [CI], 1.4 to 163; p = 0.024) and the absence of expectoration (OR, 0.14; 95% CI, 0.04 to 0.6; p = 0.006) were associated with PV pneumonia compared to pneumococcal CAP.

CONCLUSION

RVs are frequent etiologies of CAP (single or in combination with bacteria). Patients with CHF have an increased risk of acquiring a viral CAP.

Vaccination and atherosclerosis

Atherosclerosis is an inflammatory disease. Both innate and adaptive immunity are involved in lesion formation and development. A number of antigen candidates, such as oxidized low-density lipoprotein and heat shock protein, have been associated with the inflammation and immune reaction that is part of the atherosclerotic process. Because experimental models of some other inflammatory/autoimmune diseases can be improved by vaccination, it is of interest to investigate if vaccination can also be applied to prevent or retard atherosclerosis. Indeed, the modification of immune responses in animal models can greatly affect the development and progression of atherosclerosis. This review provides an overview of our current understanding of effects and proposed mechanisms of immunization on preventing atherosclerosis.

Could influenza vaccination prevent myocardial infarction, stroke and sudden cardiac death?

Acute myocardial infarction (AMI), sudden cardiac death and atherothrombotic stroke, which share a common pathogenesis involving disrupted atherosclerotic plaque and intravascular thrombosis, vary seasonally, with peak incidence in winter months. This seasonality is similar to that of upper respiratory infections, of which 38% are due to influenza. Infections such as influenza produce many biochemical, cellular, and hemostatic changes that could predispose to plaque disruption and thrombosis. Infections, particularly of the respiratory tract, often precede AMI and stroke. Four observational studies and one small clinical trial suggest that influenza vaccination can reduce the occurrence of sudden death, AMI, and stroke by approximately 50%. Influenza vaccine is very well-tolerated. With up to 16% of adults contracting influenza each year and the vaccine reducing the incidence of influenza by 50%, influenza vaccination could make a substantial public health impact on acute cardiac and neurovascular events.

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these relationships are still just associations. Failure to confirm initial reports of serologic associations also has been common. Specific causative relationships on par with that determined between H pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C pneumoniae, the effect may result from direct vessel wall colonization that may damage the vessel either directly or indirectly by initiating immunologic responses. In other cases the effect may simply be that of enhancing the pre-existing chronic inflammatory response of the body to standard risk factors such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence pre-existing plaque by enhancing T-cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Hence chronic infection may play a role either in the initiation, progression, or the destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support an etiologic role in atherosclerosis include C pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents including other herpes viruses, influenza, other specific bacteria (such as M pneumoniae), and chronic infections with common bacterial agents (periodontal disease, chronic bronchitis, and chronic urinary tract infection, among others) [191]. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate further the potential of a variety of treatment approaches, including antibiotics.

Effect of congestive heart failure on humoral and ex vivo cellular immune responses to influenza vaccination in older adults

This study examined the effect of congestive heart failure (CHF) on immune responses to influenza vaccination (2000-2001 preparation) in three groups of older adults including healthy, Class II and Class III/IV CHF. Serum antibody titers measured by hemagglutination inhibition (HI), and interferon-gamma (IFN-gamma), interleukin-10 (IL-10) and granzyme B (GrzB) levels in ex vivo virus-activated mononuclear cell cultures showed significant responses from pre-vaccination to 4 and 12 weeks post-vaccination (P<0.01). There was a trend for lower GrzB and higher IFN-gamma and IL-10 levels in healthy versus CHF groups (P<0.06) for all viral strains at 4 weeks. HI titers did not differ between groups. In the regression model, Grz B levels were significantly predicted by the IFN-gamma:IL-10 ratio and performance on the 6 min Walk Test; age and CHF dropped out of the model. In conclusion, CHF in older adults predicts GrzB responses to influenza vaccination due to cytokine and physical ability differences.

Crosstalk between LXR and toll-like receptor signaling mediates bacterial and viral antagonism of cholesterol metabolism

The liver X receptors (LXR) alpha and beta are regulators of cholesterol metabolism and determinants of atherosclerosis susceptibility. Viral and bacterial pathogens have long been suspected to be modulators of atherogenesis; however, mechanisms linking innate immunity to cholesterol metabolism are poorly defined. We demonstrate here that pathogens interfere with macrophage cholesterol metabolism through inhibition of the LXR signaling pathway. Activation of Toll-like receptors (TLR) 3 and 4 by microbial ligands blocks the induction of LXR target genes including ABCA1 in cultured macrophages as well as in aortic tissue in vivo. As a consequence of these transcriptional effects, TLR3/4 ligands strongly inhibit cholesterol efflux from macrophages. Crosstalk between LXR and TLR signaling is mediated by IRF3, a specific effector of TLR3/4 that inhibits the transcriptional activity of LXR on its target promoters. These findings highlight a common mechanism whereby bacterial and viral pathogens may modulate macrophage cholesterol metabolism and cardiovascular disease.

Influenza

Although most influenza infections are self-limited, few other diseases exert such a huge toll of suffering and economic loss. Despite the importance of influenza, there had been, until recently, little advance in its control since amantadine was licensed almost 40 years ago. During the past decade, evidence has accrued on the protection afforded by inactivated vaccines and the safety and efficacy in children of live influenza-virus vaccines. There have been many new developments in vaccine technology. Moreover, work on viral neuraminidase has led to the licensing of potent selective antiviral drugs, and economic decision modelling provides further justification for annual vaccination and a framework for the use of neuraminidase inhibitors. Progress has also been made on developing near-patient testing for influenza that may assist individual diagnosis or the recognition of widespread virus circulation, and so optimise clinical management. Despite these advances, the occurrence of avian H5N1, H9N2, and H7N7 influenza in human beings and the rapid global spread of severe acute respiratory syndrome are reminders of our vulnerability to an emerging pandemic. The contrast between recent cases of H5N1 infection, associated with high mortality, and the typically mild, self-limiting nature of human infections with avian H7N7 and H9N2 influenza shows the gaps in our understanding of molecular correlates of pathogenicity and underlines the need for continuing international research into pandemic influenza. Improvements in animal and human surveillance, new approaches to vaccination, and increasing use of vaccines and antiviral drugs to combat annual influenza outbreaks are essential to reduce the global toll of pandemic and interpandemic influenza.

The role of infection in the pathogenesis of cardiovascular disease

Atherosclerosis is a complex, multifactorial disease. Recently, research has intensified to identify the role of various infections in the pathogenesis of atherosclerosis. Specific agents have been proposed as direct initiators or accelerators of atherosclerosis, while other infectious agents have been proposed as accelerators of atherosclerosis through nonspecific stimulation of the inflammatory cascade. Recently, the total pathogen burden concept has suggested that while each specific infection contributes only slightly to the pathogenesis of atherosclerosis, the cumulative effects of infectious agents contribute greatly. Several randomized trials evaluating antibiotic therapy in the prevention of cardiovascular events have now been completed, although results have been conflicting. This manuscript summarizes current understanding of the role of infectious agents as a trigger of inflammation, as a contributor to atherosclerosis, and the potential role of antibiotic therapy in the treatment of atherosclerosis.

Influenza vaccination and reduction in hospitalizations for cardiac disease and stroke among the elderly

BACKGROUND

Upper respiratory tract illnesses have been associated with an increased risk of ischemic heart disease and stroke. During two influenza seasons, we assessed the influence of vaccination against influenza on the risk of hospitalization for heart disease and stroke, hospitalization for pneumonia and influenza, and death from all causes.

METHODS

Cohorts of community-dwelling members of three large managed-care organizations who were at least 65 years old were studied during the 1998-1999 and 1999-2000 influenza seasons. Administrative and clinical data were used to evaluate outcomes, with multivariable logistic regression to control for base-line demographic and health characteristics of the subjects.

RESULTS

There were 140,055 subjects in the 1998-1999 cohort and 146,328 in the 1999-2000 cohort, of which 55.5 percent and 59.7 percent, respectively, were immunized. At base line, vaccinated subjects were on average sicker, having higher rates of most coexisting conditions, outpatient care, and prior hospitalization for pneumonia than unvaccinated subjects. Unvaccinated subjects, however, were more likely to have been given a prior diagnosis of dementia or stroke. Vaccination against influenza was associated with a reduction in the risk of hospitalization for cardiac disease (reduction of 19 percent during both seasons [P<0.001]), cerebrovascular disease (reduction of 16 percent during the 1998-1999 season [P<0.018] and 23 percent during the 1999-2000 season [P<0.001]), and pneumonia or influenza (reduction of 32 percent during the 1998-1999 season [P<0.001] and 29 percent during the 1999-2000 season [P<0.001]) and a reduction in the risk of death from all causes (reduction of 48 percent during the 1998-1999 season [P<0.001] and 50 percent during the 1999-2000 season [P<0.001]). In analyses according to age, the presence or absence of major medical conditions at base line, and study site, the findings were consistent across all subgroups.

CONCLUSIONS

In the elderly, vaccination against influenza is associated with reductions in the risk of hospitalization for heart disease, cerebrovascular disease, and pneumonia or influenza as well as the risk of death from all causes during influenza seasons. These findings highlight the benefits of vaccination and support efforts to increase the rates of vaccination among the elderly.

Design of the Dutch prevention of influenza, surveillance and management (PRISMA) study

Rationale and design of a study on the cost-effectiveness of the Dutch influenza vaccination campaign are described. During two influenza epidemics, about 75,000 primary care patients recommended for influenza vaccination are included. Cases have fatal or non-fatal influenza, pneumonia, otitis media, acute respiratory disease (ARD), heart failure, myocardial infarction, depression or diabetes dysregulation. Per case four controls are sampled, frequency matched on age and high-risk co-morbidity (<18 years, 18-64, >/=65 healthy, >/=65 with co-morbidity). Baseline and outcome data are retrieved from patient records. During the 1999-2000 influenza A epidemic 5891 (7.9%) high-risk children, 24,848 (33.2%) high-risk adults aged 18-64 years, 18,484 (24.7%) elderly with co-morbidity and 25,527 (34.1%) healthy elderly had been included. The mortality rate was 5.2 per 1000 and 2035 non-fatal outcome events were recorded (incidence rate 27.2/1000).

Influenza vaccinations: who needs them and when?

Influenza vaccination programmes should aim at reducing the burden from influenza among those who need it most. The primary aim of this literature review is to identify who should receive priority in influenza vaccination programmes. Risk factors for severe post-influenza complications include immune-related factors, such as ageing or the presence of immune-suppression, respiratory tract disease, proneness to exacerbation of concomitant high-risk disease, potential adverse effects associated with long-term drug use or residence in closed communities with high transmission rate. When given annually in autumn, inactivated trivalent influenza vaccines can reduce severe complications from influenza among persons aged 65 years or older by 30-60%. Among children aged less than 7 years, notably those with asthma, the occurrence of otitis media or acute respiratory disease is reduced by 20-75% with vaccination. In addition, vaccination of residents of long-term care facilities and their personnel leads to a 42% reduction in mortality among patients. However, uncertainty remains about whether influenza vaccination can reduce complications from influenza among the large group of older children and persons of working-age with high-risk disease. To further increase the impact of prevention strategies, the development and application of clinical prediction rules to estimate absolute risks of post-influenza complications should be studied in relation to optimal vaccine delivery strategies. Furthermore, adequately powered studies should be conducted to demonstrate possible effectiveness of vaccination in reducing post-influenza complications among older children and working-age adults.

Myocardial infarction, stroke, and sudden cardiac death may be prevented by influenza vaccination

Acute myocardial infarction (AMI) and atherothrombotic stroke share a common pathogenesis involving disrupted atherosclerotic plaque and intravascular thrombosis. Both AMI and stroke have their peak incidence in winter months. Similarly, the incidence of upper respiratory infections (URIs), 38% of which are due to influenza, also peaks in winter (November and December). URIs result in many biochemical, cellular, and hemostatic changes that could predispose to plaque disruption and thrombosis. Infections, particularly URIs, frequently precede AMI and stroke. Up to 16% of persons older than 60 years of age experience a URI each year. Nineteen percent of those suffering an AMI recall a URI in the 2 weeks prior to their event. Three epidemiologic and one small clinical trial suggest that influenza vaccination is associated with a 50% reduction in incidence of sudden cardiac death, AMI, and ischemic stroke. Influenza vaccine is extremely safe and has a 50% efficacy. Theoretically, up to 104,500 AMIs and 192,000 nonembolic ischemic strokes could be prevented each year by influenza vaccination.

Influenza vaccine delivery and effectiveness in end-stage renal disease

BACKGROUND

Influenza vaccination rates in the general population have been associated with improved outcomes, yet high-risk populations, such as end-stage renal disease (ESRD) patients, have received little attention in determining the potential benefits. This report assessed the frequency and effectiveness of influenza vaccination, while also assessing disparities in vaccination rates in the ESRD population.

METHODS

Using the United States Renal Data System research files containing claims for all Medicare ESRD patients, vaccination rates and outcomes among vaccinated and unvaccinated persons for the 1997 to 1998 and 1998 to 1999 influenza seasons were compared after adjustment for baseline demographic factors and health characteristics.

RESULTS

Vaccination rates in the ESRD population were less than 50% for each season. Influenza vaccination rates were lower in non-whites, women, younger patients, and peritoneal dialysis patients. Influenza vaccination was associated with a lower risk for hospitalization and death.

CONCLUSIONS

Despite universal coverage of free influenza vaccination, the ESRD population had a less than 50% vaccination rate for the years 1997 to 1998 and 1998 to 1999 as demonstrated by Medicare billing data. Substantial differences were found in vaccination rates among non-whites and peritoneal dialysis patients. This study confirms that the ESRD populations benefit from influenza vaccination, suggesting that dialysis providers should take advantage of all opportunities to immunize this high-risk group.

The information network of senior citizens in Geneva, Switzerland, and progress in flu vaccination coverage between 1991 and 2000

Switzerland has lagged behind other industrialized countries in increasing vaccination coverage against flu in the elderly population. The information campaign "United against Flu", started in Geneva in 1993, gradually extended to other French and Italian speaking cantons in Switzerland and indirectly affected German-speaking cantons. Activities developed include the production of TV spots, press conferences, information forwarded to health professionals, an Internet site and information material such as leaflets and posters to risk groups. The campaign is evaluated by repeated surveys that measure vaccination coverage as well as network of informants, knowledge and perceptions in the geriatric population. Vaccination coverage of the geriatric population in Geneva canton has increased from 29% in 1991 to 59% in the year 2000.

Measurement of Chlamydia pneumoniae-specific immunoglobulin A (IgA) antibodies by the microimmunofluorescence (MIF) method: comparison of seven fluorescein-labeled anti-human IgA conjugates in an in-house MIF test using one commercial MIF and one enzyme immunoassay kit

For the serological diagnosis of acute Chlamydia pneumoniae infection, the microimmunofluorescence (MIF) test is the most commonly used method and also the "gold standard" for the measurement of immunoglobulin G (IgG) and IgM antibodies. The role of IgA antibodies in diagnosis has not been established. Commercially available fluorescein-labeled anti-human IgA conjugates have not been systematically compared to each other, and this situation may cause considerable variations in IgA results. Therefore, we tested 261 serum samples from 122 patients with pneumonia for IgA antibodies by using six alpha-chain-specific anti-IgA conjugates in our in-house MIF test, one commercial MIF test, and one enzyme immunoassay (EIA). Interfering IgG antibodies were removed with Gullsorb reagent before the measurement of IgA antibodies. Altogether, 14 significant IgA antibody increases in serum samples between the acute phase and the convalescent phase were detected by at least one of the conjugates in the MIF test, while no increases were found in the IgA EIA. Only one patient showed a significant IgA antibody increase with all of the fluorescein-labeled conjugates. Five significant titer changes were detected by at least two conjugates, and in nine instances, the titer increase was detected by one conjugate only. The titer agreement indicated by kappa coefficients was very good or good for all of the fluorescein-labeled conjugates and the EIA with low antibody titers but decreased with increasing titers.

Vacunación antigripal en pacientes con síndromes coronarios agudos: beneficio del tratamiento en diferentes subgrupos

BACKGROUND

The first prospective clinical Flu Vaccination in Acute Coronary Syndromes (FLUVACS) Trial has provided some evidence that flu vaccination together with standard therapy may be useful during the winter season to reduce the risk of death and major cardiac events in patients with acute myocardial infarction.

PATIENTS AND METHOD

Information available in the FLUVACS database was analyzed to evaluate the efficacy of flu vaccination in different subgroups. Logistic regression was used to identify features related with better therapeutic results.

RESULTS

Flu vaccination was effective in reducing the incidence of the composite endpoint (death, nonfatal myocardial reinfarction or recurrent angina prompting urgent revascularization) in most subgroups at 6 months after inclusion. The regression model showed a greater benefit of flu vaccination in patients with no ST-segment elevation or older than 65 years, nonsmokers and patients with a TIMI risk score higher than 6.

CONCLUSIONS

Our data suggest that vaccination for secondary prevention of flu during the acute phase of myocardial infarction may be effective in a broad range of patients with acute coronary artery disease, regardless of their initial clinical risk.

Influenza A and B IgG seropositivity and coronary atherosclerosis assessed by angiography

Infectious agents, in particular intracellular pathogens that can establish long-term, persistent seropositivity, may play an important role in atherogenesis. The possible association between influenza type A and B infection and angiographically proven coronary artery disease (CAD) and the effect of the aggregate pathogen burden on CAD was studied by testing blood from 218 patients undergoing coronary angiography for serum IgG antibodies to influenza A and B, and for antibodies to four other pathogens (hepatitis A, Chlamydia pneumoniae, Helicobacter pylori, and cytomegalovirus). This analysis demonstrates that although influenza (A and B) seropositivity represents no predictor of risk for CAD, infectious burden is independently associated with coronary atherosclerosis.

[Secondary prevention of coronary artery disease. Flu vaccinations and new evidence of the role of infection in acute coronary syndromes]

Recent reports have detected an increase in the number of patients with acute coronary syndromes during the flu season. More recently, case-control studies of patients with prior infarction have shown that flu vaccination significantly reduces the risk of myocardial necrosis and strokes. The World Health Organization recommended flu vaccination for the Southern Hemisphere in the winter of 2001. We evaluated the preventive impact of flu vaccination on subsequent ischemic events in myocardial infarction patients and in subjects undergoing scheduled percutaneous coronary angioplasty. In the first study we included 200 myocardial infarction patients admitted in the first 72 hours and 100 patients scheduled for angioplasty/stent (PCI) without unstable coronary artery disease, prior bypass surgery, angioplasty or tissue necrosis, were included in a prospective, multicenter registry, during the winter season. Infarction patients received standard therapy, and then were randomly allocated in a single-blind manner as a unique intramuscular Influenza vaccination or as controls. Similarly, PCI patients were allocated to either vaccination or control. The first primary outcome -cardiovascular death- occurred within 6 months in 2% of the patients in the vaccinnated group vs 8% of controls (RR: 0.25; 95% CI, 0.07-0.86; p = 0.01). The triple composite end point occurred in 11% of the patients in the vaccinnated group vs 23% of controls (p = 0.009) at 6 months. Although our study is the first to demonstrate lower rates of cardiovascular ischemic events in patients vaccinated against Influenza during the flu season, the modification of flu vaccination recommendations in patients admitted for cardiovascular events merits further study before being considered.

The role of inflammation and infection in the pathogenesis and evolution of coronary artery disease

Inflammation plays a major role in the initiation and progression of coronary artery disease (CAD) and the precipitation of acute coronary events. However, the inflammatory triggers are poorly understood. Noninfectious stimuli undoubtedly play a role. Recently, chronic infection has been proposed as another inflammatory trigger. Histologically, unstable atherosclerotic plaque contains activated macrophages and T lymphocytes, adhesion molecules, chemokines and cytokines, matrix-degrading enzymes, and prothrombotic factors. Circulating inflammatory markers such as C-reactive protein, fibrinogen, and interleukins are increased in high-risk cohorts and predict future risk. Experimental models and human studies have supported a role of infection in the promotion of atherosclerosis. Although the independent predictive value of seropositivity to individual agents has varied, total pathogen burden, the sum of seropositivities to many bacterial and viral vectors, has been more consistent. Whether antibiotics or vaccines will be useful in CAD prevention remains to be shown. Meanwhile, therapies with proven vascular anti-inflammatory effects (eg, diet, exercise, smoking cessation, aspirin, statins) should be optimized.

Infections and their role in atherosclerotic vascular disease

BACKGROUND

Complications of atherosclerosis are the leading cause of mortality in developed countries, and infections may play a role in the pathogenesis. Numerous studies have addressed this issue in the past decade.

TYPES OF STUDIES REVIEWED

The author examined peer-reviewed studies and reviews on the role of microbes or infections in atherosclerosis, cardiovascular disease and cerebrovascular disease. He included selected articles on epidemiology, pathology, in vitro experiments, animal models and clinical studies.

RESULTS

Cross-sectional and retrospective studies have shown an association between Chlamydia pneumoniae antibodies and cardiovascular disease, but prospective studies have not been as convincing. Studies on the association between cardiovascular disease and periodontal disease or loss of teeth have produced conflicting results. Cytomegalovirus infection is associated mainly with accelerated arteriosclerosis after cardiac transplantation. Infectious agents can induce biological mechanisms important for atherogenesis. Mice and rabbit studies have indicated that C. pneumoniae is capable of initiating or accelerating the progression of atherosclerosis. Limited studies on cytomegalovirus also suggest the ability to induce early changes of atherosclerosis in a rodent model. Preliminary clinical trials of treatment for C. pneumoniae infection suggest a possible short-term benefit, but larger randomized trials for longer periods are in progress.

CONCLUSION AND CLINICAL IMPLICATIONS

Infectious agents may play an important role in atherogenesis, but currently the jury is not in. Further management of cardiovascular disease could change radically if this concept were proven.

Chronic infections and atherosclerosis/thrombosis

An emerging pathophysiologic paradigm implicates chronic inflammation in the initiation, progression, and destabilization of atherosclerotic vascular disease. Various potential contributors to the inflammatory response in the vessel wall include atherogenic lipids, mechanical stress and injury, hypertension and angiotensin II, cigarette smoking, immune response to neoantigens, and chronic infections with viruses and or bacteria (Table 1). The potential link between chronic infection and atherosclerosis/thrombosis is under extensive investigation in several laboratories around the world. Although indirect evidence and experimental data tend to support this link, definitive proof is still lacking. If such a link is eventually proven to be causal in nature, it will provide a novel target for preventive and therapeutic strategies (anti-infective drugs, vaccines, etc.) against a common disease that is the leading killer of people in Western nations. Results of ongoing, large-scale clinical trials are eagerly awaited.

Case-control studies: research in reverse

Epidemiologists benefit greatly from having case-control study designs in their research armamentarium. Case-control studies can yield important scientific findings with relatively little time, money, and effort compared with other study designs. This seemingly quick road to research results entices many newly trained epidemiologists. Indeed, investigators implement case-control studies more frequently than any other analytical epidemiological study. Unfortunately, case-control designs also tend to be more susceptible to biases than other comparative studies. Although easier to do, they are also easier to do wrong. Five main notions guide investigators who do, or readers who assess, case-control studies. First, investigators must explicitly define the criteria for diagnosis of a case and any eligibility criteria used for selection. Second, controls should come from the same population as the cases, and their selection should be independent of the exposures of interest. Third, investigators should blind the data gatherers to the case or control status of participants or, if impossible, at least blind them to the main hypothesis of the study. Fourth, data gatherers need to be thoroughly trained to elicit exposure in a similar manner from cases and controls; they should use memory aids to facilitate and balance recall between cases and controls. Finally, investigators should address confounding in case-control studies, either in the design stage or with analytical techniques. Devotion of meticulous attention to these points enhances the validity of the results and bolsters the reader's confidence in the findings.

Chlamydia pneumoniae and atherosclerosis -- what we know and what we don't

The clinical manifestations of atherosclerosis include coronary artery disease (CAD), stroke, abdominal aortic aneurysm and peripheral vascular disease. World-wide, CAD and stroke are the leading causes of death and disability. The recognition of atherosclerosis as an inflammatory disease in its genesis, progression and ultimate clinical manifestations has created an interesting area of vascular research. Apart from those well-known traditional risk factors for atherosclerosis, novel and potentially treatable atherosclerotic risk factors such as homocysteine (an amino acid derived from the metabolism of dietary methionine that induces vascular endothelial dysfunction) and infections have emerged. In fact, the century-old 'infectious' hypothesis of atherosclerosis has implicated a number of micro-organisms that may act as contributing inflammatory stimuli. Although cytomegalovirus, Helicobacter pylori and Chlamydia pneumoniae are the three micro-organisms most extensively studied, this review will focus on C. pneumoniae. Collaborative efforts from many disciplines have resulted in the accumulation of evidence from seroepidemiological, pathological, animal model, immunological and antibiotic intervention studies, linking C. pneumoniae with atherosclerosis. Seroepidemiological observations provide circumstantial evidence, which is weak in most prospective studies. Pathological studies have demonstrated the preferential existence of C. pneumoniae in atherosclerotic plaque tissues, while animal model experiments have shown the induction of atherosclerosis by C. pneumoniae. Finally, immunological processes whereby C. pneumoniae could participate in key atherogenic and atherothrombotic events have also been identified. Although benefits of the secondary prevention of atherosclerosis have been demonstrated in some antibiotic intervention studies, a number of negative studies have also emerged. The results of the ongoing large prospective human antibiotic intervention trials may help to finally establish if there is a causal link between C. pneumoniae infection and atherosclerosis.