Chlamydia pneumoniae: risk factors for seropositivity and association with coronary heart disease

Is there an infective aetiology to atherosclerosis?

Conventional cardiovascular risk factors fail to completely explain the observed variations in the prevalence and severity of coronary heart disease (CHD). Common chronic infections may have an aetiological role in the development of atherosclerosis and CHD, either independently or by interacting with traditional atherogenic risk factors. The evidence for Chlamydia pneumoniae as a potential causative agent is strongest, and is based on findings of numerous sero-epidemiological studies, examination of atheromatous plaque specimens, in vitro animal models and, recently, pilot antichlamydial antibiotic intervention trials. However, the complete natural history of C. pneumoniae, its mechanisms of damage in atherosclerotic disease, and the temporal sequence of infection and CHD remain unclear. Confirmation of true causality for the link between C. pneumoniae and CHD could come after the results of large-scale prospective antibiotic trials, which are to be conducted over the next few years. A proven association could have important implications for public health worldwide, potentially leading to novel and relatively inexpensive therapeutic measures in the secondary prevention of CHD--broad-spectrum antibiotics.

Risk factors for ischemic stroke: Dubbo Study of the elderly

BACKGROUND AND PURPOSE

One in 10 deaths in Australia is due to stroke. The predictors of ischemic stroke have not been well defined, although hypertension, atrial fibrillation, and previous stroke have been consistently reported. We report on 98 months' follow-up in a prospective study of cardiovascular disease in the Australian elderly, the Dubbo Study.

METHODS

The cohort, first examined in 1988, was composed of 2805 men and women 60 years and older. The prediction of ischemic stroke by potential risk factors was examined in a Cox proportional hazards model, after linkage to hospital and death records.

RESULTS

Three hundred six men and women manifested an ischemic stroke event (ICD-9-CM 433 to 437), and 95 subjects suffered a fatal stroke event. In the multivariate model, the significant independent predictors of stroke were advancing age, female sex (48% lower risk), being married (30% lower risk), prior history of stroke (227% higher risk), use of antihypertensive drugs (37% higher risk), belonging to the highest category of blood pressure reading (67% higher risk), presence of atrial fibrillation (58% higher risk), HDL cholesterol (36% lower risk for each 1-mmol/L increment), impaired peak expiratory flow (77% higher risk for tertile I than for tertile III), physical disability (59% higher risk), and depression score (41% higher risk for tertile III than for tertile I).

CONCLUSIONS

These findings suggest that morbidity and mortality associated with ischemic stroke can be predicted by various clinical indicators, some of which may be amenable to intervention. The matters of impaired peak expiratory flow, depression score, and ischemic stroke require further study.

[Arteriosclerosis as a sequela of chronic Chlamydia pneumoniae infection]

In the last years several new data allow a controversial but convincing interpretation of the pathogenesis of atherosclerosis (arteriosclerosis). Atherosclerosis can be apparently the result of ultrachronic persistent infection by Chlamydia pneumoniae and not the result of different risk factors. The main arguments for the chlamydial genesis are: 1. Correlation of coronary heart disease and other atherosclerotic disease with antibodies against C. pneumoniae. 2. C. pneumoniae could be detected with different techniques (PCR, immunohistology, electromicroscopy, culture) in a high percentage in atheromas from different sites. 3. Three international studies with macrolides in coronary heart disease were successful. 4. The target cells of atherosclerosis (endothelia, macrophages, muscle cells) can be infected by C. pneumoniae in vitro. 5. Positive animal experiments. The Koch-Henle criteria for the proof of the etiology are largely fulfilled--even if there are doubts about the validity of these criteria in chronic local infections. A number of unexplainable aspect of atherosclerosis can be seen in a new light. The higher incidence of coronary heart disease in young males has a parallel in the remarkable androtropism of many bacterial diseases (pneumococcal pneumonia, tuberculosis). The reduction of incidence of atherosclerotic diseases since 1965 can be explained by the much higher intake of doxycyclin and macrolides. The low incidence of coronary heart disease in France--sometimes regarded as an effect of red wine--can be explained as a result of a much higher use of antichlamydial antibiotics. The increase of inflammatory parameters (C-reactive protein, fibrinogen, leucocytes) before acute coronary infarction are not risk factors but signs of an active chronic infection. The interpretation is possible, that atherogenic changes in lipids like increase of LDL and decrease of HDL are not risk factors but consequence of chronic arterial infection by chlamydia. The low incidence of atherosclerosis in the tropics--despite high frequency of chlamydial infection--is difficult to explain. Vascular infection can be related with the age of the patient at the primary infection. With low hygiene, intestinal primary infections in early childhood can be possible. Arterial infection would be thus a result of a primary infection in adolescence ("yet another poliomyelitis story"). There are good arguments for the thesis that C. pneumoniae is the primary cause of atherosclerosis and not a secondary invader. The consequence, nevertheless, is similar: Antibiotics get a key role. The macrolides roxithromycin, azithromycin, clarithromycin and the tetracyclin doxycyclin fulfill the criteria as potential antichlamydial agents. In general a longer treatment (6 to 8 to 12 weeks) seems advisable. It is necessary to start international studies with antibiotics in coronary infarction and other clinical manifestations of atherosclerosis. The relevant antibiotics licensed for chlamydial infections are cheap and safe. Despite of the urgent need for controlled studies, it seems already justified to treat high-risk patients with antibiotics. Meticulous protocols and long-term control of patients are necessary to evaluate the therapeutic effects. Preventive studies in patients without clinical manifestation of atherosclerosis are urgently needed. The risks of resistance or side effects are neglectable, but the organisation of such studies would be very difficult.

Failure to detect Chlamydia pneumoniae in atherosclerotic plaques of Australian patients

Chlamydia pneumoniae is a recently reported, but common, respiratory tract pathogen. The organism has been detected by electron microscopy, immunocytochemistry, polymerase chain reaction (PCR) and recently culture within atherosclerotic plaques, suggesting a possible association between C. pneumoniae infection and atherosclerosis. Interestingly this association has not been found by all researchers. We examined 17 carotid endarterectomy specimens, 16 carotid arteries and 16 coronary arteries from autopsy specimens. They were examined by PCR for the presence of C. pneumoniae. In none of the 49 atherosclerotic samples examined was C. pneumoniae detected. The sensitivity of our PCR assay was rigorously tested and found to detect consistently fewer than ten elementary bodies. The association between C. pneumoniae and atherosclerosis is intriguing but has not yet been demonstrated in Australian patients.

Distribution of Chlamydia pneumoniae infection in the athersclerotic carotid artery

BACKGROUND AND PURPOSE

Chlamydia pneumoniae infection has recently become noteworthy in relation to atherosclerosis. We investigated by immunohistochemistry the distribution of C pneumoniae infection in the atherosclerotic carotid artery.

METHODS

Twenty carotid atherosclerotic lesions that were resected during carotid endarterectomy were investigated. Parallel sections were stained immunohistochemically with monoclonal antibodies for a C pneumoniae-specific antigen, macrophages, and smooth muscle cells.

RESULTS

Immunoreactivity for the C pneumoniae-specific antigen was observed in 11 of 20 specimens (55%), and intense immunoreactivity was observed in 7 of 20 (35%). C pneumoniae infection was observed in endothelial cells, macrophages and in smooth muscle cells that had migrated into the atheromatous plaque, as well as in smooth muscle cells and small arteries in the media underlying the atheromatous plaques. C pneumoniae infection was most prominently observed in smooth muscle cells. The severity of the infection as demonstrated by immunohistochemistry was not significantly related to general risk factors for atherosclerosis.

CONCLUSIONS

C pneumoniae widely infects endothelial cells, macrophages, and smooth muscle cells in the atherosclerotic carotid artery. The results of the present study can help us to understand how C pneumoniae infection contributes to the progression of carotid atherosclerosis.

Comparison of throat swabs with sputum specimens for the detection of Chlamydia pneumoniae antigen by direct immunofluorescence

AIM

To compare throat swabs with sputum specimens for Chlamydia pneumoniae antigen detection.

METHODS

During a one year period, sputum and throat swabs from 50 patients over 15 years of age with acute or persisting lower respiratory tract infection were examined for C pneumoniae antigen by direct immunofluorescence.

RESULTS

C pneumoniae antigen was detected in 18/50 patients (36.0%) from sputum, throat swab, or both. Paired sputum and throat swabs were received from 35/50 patients (70.0%). C pneumoniae antigen was detected in either or both specimens from 14/35 patients (40.0%). Of the 14 positive patients, both specimens were positive in nine (64.3%), throat swab only in four (28.6%), and sputum only in one (7.1%). Of the remaining 15 patients from whom only a single specimen was sent, a further three of eight throat swabs and one of seven sputum specimens were positive. There was no statistically significant difference between the results obtained from the two types of specimen.

CONCLUSIONS

Throat swabs may be as good as sputum for the detection of C pneumoniae antigen.

Endovascular presence of viable Chlamydia pneumoniae is a common phenomenon in coronary artery disease

OBJECTIVES

We sought to examine coronary arteries for the presence of viable bacteria of the fastidious species Chlamydia pneumoniae.

BACKGROUND

The respiratory pathogen C. pneumoniae has been implicated in the pathogenesis of coronary artery disease (CAD). Previous studies have demonstrated an antichlamydial seroresponse to be a cardiovascular risk factor and coronary atheromata to contain chlamydial components in varying proportions. Endovascular demonstration of replicating bacteria is required to provide evidence for an infectious component in CAD and a rationale to discuss antimicrobial therapy.

METHODS

Myocardial revascularization was performed in 70 patients. Atherosclerotic lesions from 53 coronary endarterectomy and 17 restenotic bypass samples were cultured and subjected to nested polymerase chain reaction (PCR) for C. pneumoniae. Antichlamydial immunoglobulin G (IgG), IgA and IgM was examined by microimmunofluorescence.

RESULTS

Viable C. pneumoniae was recovered from 11 (16%) of 70 atheromata, and chlamydial deoxyribonucleic acid (DNA) was detected in 21 (30%) of 70 atheromata; 17 nonatherosclerotic control samples were PCR-negative (p < 0.01). Fifteen (28%) of 53 endarterectomy and 6 (35%) of 17 bypass samples were PCR-positive. DNA sequencing of six different PCR products did not reveal differences between coronary isolates and respiratory reference strains, suggesting that common respiratory strains gain access to the systemic circulation. Serologic results did not correlate with direct detection results and did not identify individual endovascular infection.

CONCLUSIONS

A significant proportion of atherosclerotic coronary arteries harbor viable C. pneumoniae. This finding supports the hypothesis of a chlamydial contribution to atherogenesis. Whether chlamydiae initiate atherosclerotic injury, facilitate its progression or colonize atheromata is unknown. However, the endovascular presence of viable bacteria justifies a controlled clinical investigation of antimicrobial treatment benefit in the therapy and prevention of CAD.

Fundamentals of clinical methodology: 2. Etiology

The concept of etiology is analyzed and the possibilities and limitations of deterministic, probabilistic, and fuzzy etiology are explored. Different kinds of formal structures for the relation of causation are introduced which enable us to explicate the notion of cause on qualitative, comparative, and quantitative levels. The conceptual framework developed is an approach to a theory of causality that may be useful in etiologic research, in building nosological systems, and in differential diagnosis, therapeutic decision-making, and controlled clinical trials. The bearings of the theory are exemplified by examining the current Chlamydia pneumoniae hypothesis on the incidence of myocardial infarction.

Chlamydia pneumoniae and its role in chronic obstructive pulmonary disease

The diverging of T-helper (Th) cells into predominantly Th1 and Th2 subsets on the basis of their cytokine profiles has decisively improved our understanding of the pathogenesis of many chronic infectious diseases. Recent data suggest that the presence of interferon-gamma and the subsequent suppression of interleukin-4 production leads to a Th1-type response that is required for the resolution of infections caused by intracellular pathogens. The ability of the macrophages to respond aggressively during early antigen contact seems to be one crucial factor in the development of an appropriate Th-cell response. Several host-related factors can affect macrophage function and the polarization of T-cell responses, ie the shift from a Th1 response to a Th2 one, and thus dramatically deteriorate the resolution of infections caused by intracellular agents such as Chlamydia pneumoniae. Chronic C. pneumoniae infection has been associated with several common chronic diseases, quite recently with chronic obstructive pulmonary disease. Chronic C. pneumoniae infection may amplify smoking-associated inflammation in the bronchi and may be a contributory factor in the development of irreversible pathological changes.

Chlamydia pneumoniae, cytomegalovirus, and herpes simplex virus in atherosclerosis of the carotid artery

BACKGROUND

Chlamydia pneumoniae and the herpes viruses cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV-1) have been associated with human atherosclerosis in seroepidemiological and separate histopathological studies. We investigated the concurrent presence of these microorganisms in patients undergoing carotid endarterectomy.

METHODS AND RESULTS

Endarterectomy specimens from 76 patients with carotid artery stenosis were stained for C. pneumoniae, CMV, and HSV-1 particles with specific IgG monoclonal antibodies by the avidin-biotin-peroxidase method. IgG antibodies to CMV and C. pneumoniae were also measured in the serum. These were correlated with plaque morphology and the presence of the microorganisms in the atherosclerotic plaques. C. pneumoniae was detected in 54 (71%) (95% confidence interval [CI], 59.5% to 80.9%), CMV was detected in 27 (35.5%) (CI, 24.9% to 47.3%), and HSV-1 was detected in 8 (10.5%) (CI, 4.7% to 19.7%) versus none of 20 (0%) control normal carotid artery and aortic tissue (autopsy) specimens (CI, 0% to 16.8%) (P<.001 for CMV and C. pneumoniae). At least one microorganism was detected in 59 of the specimens (77.6%) (CI, 66.6% to 86.4%), with a single microorganism present only in 35 (46%), two microorganisms present in 18 (23.7%) (CI, 14.7% to 34.8%), and all three present in 6 (7.9%) (CI, 3.0% to 16.4%). Atherosclerotic plaques with thrombosis were more likely to have C. pneumoniae (80.4%) or CMV (57.8%) than were plaques without thrombosis (56.7% and 16.7%, respectively; P=.04 and .007). There was no correlation between the presence of CMV and C. pneumoniae in the atherosclerotic vessels and serum antibody titers.

CONCLUSIONS

C. pneumoniae and CMV are commonly detected in atherosclerotic plaques of the carotid arteries, but their presence cannot be predicted by measuring serum antibodies. The presence of these microorganisms may predispose to a greater risk of thrombosis in the plaques, but further studies are needed to confirm this observation.

Cardiovascular disease risk from prior Chlamydia pneumoniae infection can be related to certain antigens recognized in the immunoblot profile

Chlamydia pneumoniae infection has been described as a risk factor for atherosclerosis on the basis of raised seroreactivity against complete elementary bodies among cardiovascular disease (CVD) patients. In order to identify antigens of possible pathogenetic relevance, C. pneumoniae IgG and IgA immunoblot profiles were compared for CVD patients (IgG: n = 159; IgA: n = 72) and for controls (IgG: n = 158; IgA: n = 115), all with prior C. pneumoniae infection. IgG and IgA recognition patterns were very similar, and a broad range of antigens was commonly recognized. However, statistical analysis demonstrated IgG seroresponses to 40, 54, 60, 75, and 98 kDa antigens to be more frequent among patients and resulting in odds ratios between 2.3 (98 kDa) and 29.4 (40 kDa) for development of CVD. This relation remained evident after adjustment for age and sex. Cardiovascular risk from prior chlamydial infection can thus be linked to certain antigens. Thus, for the first time potential atherogenetic virulence factors of C. pneumoniae are described. Though causal relation of chlamydial and atherosclerotic disease cannot be proven yet, evidence is growing that chlamydial structures play a part in the multifactorial pathogenesis of one of the most prevalent health hazards world-wide.

A possible association of Chlamydia pneumoniae infection and acute myocardial infarction in patients younger than 65 years of age

STUDY OBJECTIVES

We conducted a retrospective study on patients with acute myocardial infarction (AMI) and evaluated the incidence and prevalence of Chlamydia pneumoniae infection.

METHODS

Sixty-one consecutive patients with AMI aged younger than 65 years were enrolled. Within 24 h of hospital admission, serum samples and pharyngeal swab specimens were obtained from all patients. In 49 of 61 patients, after a mean of 28 days from hospital admission, a second serum sample was drawn. A third serum sample was obtained in 23 of 61 patients. Serologic testing for Chlamydia pneumoniae was performed by a microimmunofluorescence test. We applied a nested-polymerase chain reaction for C pneumoniae DNA detection to pharyngeal swab specimens. Simultaneously, we performed a serologic study for C pneumoniae infection on 61 serum samples obtained from blood donors, matched for age, sex, and smoking habits.

RESULTS

Serologic test results for C pneumoniae were consistent with acute reinfection in 12 patients, with chronic infection in 23 patients, and results were negative in 26 patients with AMI. In 3 of 12 patients with acute reinfection pattern and in 3 of 23 patients with chronic infection pattern, C pneumoniae DNA was detected on pharyngeal swab specimens. A significantly higher prevalence of IgG titers was observed in patients with AMI (35/61) compared to blood donors (18/61) (p=0.003).

CONCLUSION

Our data confirm the possible role of C pneumoniae infection in coronary heart disease and suggest that reinfection may trigger the onset of AMI.

Elevated Chlamydia pneumoniae antibodies, cardiovascular events, and azithromycin in male survivors of myocardial infarction

BACKGROUND

The clinical significance of the association between elevated anti-Chlamydia pneumoniae (Cp) antibody titres and coronary heart disease (CHD) is unclear. We explored the relationship between antibodies against Cp and future cardiovascular events in male survivors of myocardial infarction (MI). The effect of azithromycin antibiotic therapy was assessed in a subgroup of post-MI patients.

METHODS AND RESULTS

We screened 220 consecutive male survivors of MI for anti-Cp antibodies. Of these, 213 patients were stratified into three groups: group Cp-ve (n=59), no detectable Cp antibodies; group Cp-I (n=74), intermediate titres of 1/8 to 1/32 dilution; and group Cp+ve (n=80), seropositive at > or = 1/64 dilution. Patients with persisting seropositivity of > or = 1/64 were randomized to either oral azithromycin (Cp+ve-A, 500 mg/d for 3 days [n=28] or 500 mg/d for 6 days [n=12]) or placebo (Cp+ve-P, n=20). Cp+ve-NR (n=20) represented patients not recruited into the antibiotic trial. The incidence of adverse cardiovascular events (over a mean follow-up period of 18+/-4 months) was recorded and shown to increase with increasing anti-Cp titre: Cp-ve, n=4 (7%); Cp-I, n=11 (15%); Cp+ve-NR, n=6 (30%); and Cp+ve-P, n=5 (25%). Cp+ve-NR and Cp+ve-P groups had a fourfold-increased risk for adverse cardiovascular events compared with the Cp-ve group (odds ratio [OR], 4.2; 95% confidence interval [CI], 1.2 to 15.5; P=.03). In contrast, the OR for cardiovascular events in patients receiving azithromycin (Cp+ve-A, single or double course) was the same as in the Cp-ve group (OR, 0.9; 95% CI, 0.2 to 4.6, P=NS). Patients receiving azithromycin were more likely to experience a decrease in IgG anti-Cp titres than were those in the placebo group (P=.02).

CONCLUSIONS

An increased anti-Cp antibody titre may be a predictor for further adverse cardiovascular events in post-MI patients. Taking a short course of azithromycin may lower this risk, possibly by acting against Cp.

Relationship of peak expiratory flow rate with mortality and ischaemic heart disease in elderly Australians

OBJECTIVE

To evaluate the relationships of mortality and ischaemic heart disease (IHD) with peak expiratory flow rate (PEF) in the elderly.

DESIGN

Prospective study with median follow-up of 83 months.

SETTING

Dubbo, a New South Wales country town (population, 30500).

SUBJECTS

Non-institutionalised residents born before 1930 (i.e., aged 60 years and over at study entry). Participation rate was 73% (1235 men and 1570 women).

MAIN OUTCOME MEASURES

Baseline demographic, psychosocial and standard cardiovascular risk factors, including PEF; all-causes mortality, IHD mortality and IHD events (hospitalisations with any manifestation of IHD) by tertile of PEF.

RESULTS

More subjects with PEF in the lowest tertile (I) had a past history of respiratory disease, were current cigarette smokers and were taking antihypertensive drugs. During follow-up, 321 men (26%) and 252 women (16%) died. All-causes mortality was three (men) to four (women) times higher for those in PEF tertile I than for those in tertile III. IHD mortality and IHD events showed similar trends. In a proportional hazards model adjusted for age, height, smoking status and other risk factors or confounders, the hazard ratios (95% confidence interval) for men in PEF tertile I versus tertile III were: all-causes mortality, 1.62 (1.14-2.30); IHD mortality, 1.75 (0.96-3.20); and IHD events, 1.12 (0.82-1.53). For women, respective hazard ratios were 1.92 (1.23-3.00), 2.58 (1.24-5.39), and 1.16 (0.83-1.63).

CONCLUSIONS

We confirm an independent, inverse relationship between PEF and all-causes and IHD mortality. The data suggest a potential benefit for coronary risk factor management in subjects with existing airways disease and further support the case for antismoking programs.

Rabbit model for Chlamydia pneumoniae infection

A rabbit model was established for Chlamydia pneumoniae infection that may be helpful to understand the pathogenesis of disease in humans. Twelve, pathogen-free, 1-month-old New Zealand White rabbits were inoculated with 1.0 x 10(7) to 5.0 x 10(7) CFU of purified C. pneumoniae (ATCC strain VR 1310) via the nasopharynx (1 rabbit died immediately postinoculation, and 11 were available for study). Five controls were inoculated with the carrier buffer. Ten of the 11 study rabbits demonstrated serological evidence of acute infection (immunoglobulin G antibodies, 1:8 to > 1:16), with the weakest response at 7 days and the strongest response at 28 days, whereas none of the controls showed any seroconversion. Study animals were sacrificed in batches of three, on days 7, 14, 21, and 28, but controls were sacrificed on days 7 and 28. Two-thirds of the animals demonstrated evidence of bronchiolitis and pneumonia on days 7 and 14 and resolution by day 21. Two study rabbits demonstrated, on histology, early and intermediate lesions of atherosclerosis: one animal (day 7) showed the accumulation of foamy macrophages (fatty streak) in the arch of the aorta, and the other animal (day 14) showed spindle cell proliferation of smooth muscle cells (intermediate lesion). Focal periaortitis was seen in the same animal (day 7). C. pneumoniae elementary bodies were demonstrated by immunocytochemical stain in the lungs (n = 2), liver (n = 3), spleen (n = 5), and aorta (n = 2), one of which corresponded to the intermediate lesion. C. pneumoniae was cultured from the lungs (n = 2), liver (n = 2), spleen (n = 2), and aortic arch (n = 1). All histopathological, immunocytochemical, and cultural studies were negative in the controls. Hence, the rabbit provides a useful animal model for the study of C. pneumoniae infection and its complications, particularly atherosclerosis.

Association of chlamydial infection with cerebrovascular disease

BACKGROUND AND PURPOSE

Recent studies suggest an association of coronary heart disease and carotid atherosclerosis with Chlamydia pneumoniae infection. We investigated the frequency of chlamydial seropositivity and specific circulating immune complexes in patients with recent cerebrovascular disease.

METHODS

Specific antibodies to C pneumoniae in serum were measured by the microimmunofluorescence test in 58 consecutive patients (aged 18 to 50 years) with ischemic infarction (n = 39) or transient ischemic attacks (n = 19) and in 52 hospital control subjects without vascular disease, matched for sex, age, time, and locality.

RESULTS

Twenty-seven patients (46.6%) and 12 control subjects (23.1%) had raised IgA titers > or = 1:16 (P = .018). IgG titers > or = 1:32 were measured in 74.1% of the patients and 77% of control subjects (P = .623). Specific IgG antibodies in circulating immune complexes, which were isolated by polyethylene glycol precipitation, were elevated > or = 1:8 in 24.1% of the patients and 7.7% of control subjects (P = .047). With the use of a conditional logistic regression model, the odds ratios were 1.70 (95% confidence interval [CI], 1.13 to 2.58) for elevated IgA titers, 1.91 (95% CI, 1.06 to 3.47) for the presence of immune complexes, and 1.96 (95% CI, 1.00 to 3.82) for the presence of both factors. After adjustment for the vascular risk factors hypertension, age, sex, and migraine, the odds ratios were 1.71 (95% CI, 1.08 to 2.70), 2.00 (95% CI, 1.07 to 3.76), and 2.20 (95% CI, 1.09 to 4.41), respectively.

CONCLUSIONS

We conclude that chronic infection with C pneumoniae is associated with an increased risk of stroke and transient ischemic events.

Symptoms of chronic bronchitis and the risk of coronary disease

BACKGROUND

Experimental and epidemiological studies show a positive association between coronary disease and various infections in different organs, both viral and bacterial and both acute and chronic. Most attention has been paid to dental infections and infections in the respiratory tract. We have studied how chronic respiratory infection predicts coronary disease.

METHODS

We defined chronic respiratory infection by the occurrence of symptoms of chronic bronchitis. We also analysed whether any association with coronary disease incidence and mortality is independent of the known major cardiovascular risk factors and whether it is similar among persons in different occupations. Our cohort study was a 13-year follow-up of 19,444 randomly selected eastern Finnish men and women born between 1913 and 1947 and examined in either 1972 or 1977.

FINDINGS

During follow-up, there were 1419 first coronary events, either fatal or non-fatal, and 614 coronary deaths. Among men, the age-adjusted and study-year-adjusted risk ratio of long lasting-symptoms of chronic bronchitis (during as much as 3 months in a year) was 1.52 (95% CI 1.33-1.75) for coronary disease and 1.74 (CI 1.43-2.11) for coronary death. Among women the risk ratios were 1.38 (1.07-1.78) and 1.49 (0.98-2.27), respectively. Inclusion of smoking, serum cholesterol, and systolic blood pressure into the models decreased risk ratios to 1.36 (1.17-1.56) and 1.55 (1.26-1.90) in men and to 1.34 (1.04-1.74) and 1.41 (0.92-2.16) in women, respectively. The risk of coronary disease associated with the symptoms of chronic bronchitis was similar among blue-collar and white-collar workers but the association was not found among farmers.

INTERPRETATION

Symptoms of chronic bronchitis predicted the risk of coronary disease independently from the known major cardiovascular risk factors. If the observed association is causal, prevention and improved management of chronic infections may have played a role in the decrease in coronary disease mortality observed in eastern Finland in the past two decades.

Chlamydia pneumoniae and cardiovascular diseases

Chlamydia infection of the cardiovascular system is associated with pericarditis, endocarditis and myocarditis. Chlamydia particles can also be observed in damaged heart valves. There is now good evidence that the lesions of arteriosclerosis and aortic aneurysm as well as valvular disease may be associated with C. pneumoniae infection. Patients with acute myocardial infarction show seroconversion against Chlamydia lipopolysaccharide. In a prospective study of 4000 healthy hypercholesterolemic men, signs suggestive of chronic C. pneumoniae infection increased the risk of a cardiac event three---fold. This risk factor is synergistic with the smoking risk. Immunohistochemistry also demonstrated Chlamydia lipopolysaccharide in samples of aortic aneurysm. Chlamydial inflammation may play a role in the oxidation of low density lipoprotein in atherosclerotic lesions.

The immunobiology and immunopathology of chlamydial infections

Chlamydiae are obligate intracellular bacterial pathogens of eukaryotic cells responsible for a wide variety of important human and animal infections. In humans, chlamydial infections are generally localised to superficial epithelial or mucosal surfaces, are frequently asymptomatic and may persist for long periods of time if untreated, inducing little protective immunity. Nevertheless, neutralising antibodies of limited efficacy are produced against the main chlamydial outer envelope protein, while gamma interferon (IFN gamma) is chlamydiastatic and paradoxically may play a role both in chlamydial persistence and in protective immunity. Delayed hypersensitivity responses to chlamydiae caused by repeated or persistent infection are thought to be important in the development of the severe scarring sequelae characteristic of cicatricial trachoma and of chronic salpingitis. Chlamydial heat shock proteins bearing close homology with their human equivalents may be major targets for immunopathological responses and their expression is upregulated in IFN gamma induced persistent infection. C. pneumoniae, a common cause of acute respiratory infection in humans, may persist in coronary arteries and is strongly implicated as a risk factor in atherosclerosis and in acute myocardial infarction. This paper reviews the immunology and immunopathology of chlamydial infections in the context of the unique biology of this fascinating but challenging group of organisms.

Association of Helicobacter pylori and Chlamydia pneumoniae infections with coronary heart disease and cardiovascular risk factors

OBJECTIVE

To investigate the relation between seropositivity to chronic infections with Helicobacter pylori and Chlamydia pneumoniae and both coronary heart disease and cardiovascular risk factors.

DESIGN

Cross sectional study of a population based random sample of men. Coronary heart disease was assessed by electrocardiography, Rose angina questionnaire, and a history of myocardial infarction; serum antibody levels to H pylori and C pneumoniae were measured, risk factor levels determined, and a questionnaire administered.

SETTING

General practices in Merton, Sutton, and Wandsworth, south London.

SUBJECTS

388 white south London men aged 50-69.

MAIN OUTCOME MEASURES

Evidence of coronary risk factors and infection with H pylori or C pneumoniae.

RESULTS

47 men (12.1%) had electrocardiographic evidence of ischaemia or infarction. 36 (76.6%) and 18 (38.3%) were seropositive for H pylori and C pneumoniae, respectively, compared with 155 (45.5%) and 62 (18.2%) men with normal electrocardiograms. Odds ratios for abnormal electrocardiograms were 3.82 (95% confidence interval 1.60 to 9.10) and 3.06 (1.33 to 7.01) in men seropositive for H pylori and C pneumoniae, respectively, after adjustment for a range of socioeconomic indicators and risk factors for coronary heart disease. Cardiovascular risk factors that were independently associated with seropositivity to H pylori included fibrinogen concentration and total leucocyte count. Seropositivity to C pneumoniae was independently associated with raised fibrinogen and malondialdehyde concentrations.

CONCLUSIONS

Both H pylori and C pneumoniae infectins are associated with coronary heart disease. These relations are not explained by a wide range of confounding factors. Possible mechanisms include an increase in risk factor levels due to a low grade chronic inflammatory response.