Identfication of viral and bacterial etiologic agents of the pertussis-like syndrome in children under 5 years old hospitalized.

BACKGROUND: Acute respiratory infections (ARIs) represent an important cause of morbidity and mortality in children, remaining a major public health concern, especially affecting children under 5 years old from low-income countries. Unfortunately, information regarding their epidemiology is still limited in Peru. METHODS: A secondary data analysis was performed from a previous cross-sectional study conducted in children with a probable diagnosis of Pertussis from January 2010 to July 2012. All samples were analyzed via Polymerase Chain Reaction (PCR) for the following etiologies: Influenza-A, Influenza-B, RSV-A, RSV-B, Adenovirus, Parainfluenza 1 virus, Parainfluenza 2 virus, Parainfluenza 3 virus, Mycoplasma pneumoniae and Chlamydia pneumoniae. RESULTS: A total of 288 patients were included. The most common pathogen isolated was Adenovirus (49%), followed by Bordetella pertussis (41%) from our previous investigation, the most prevelant microorganisms were Mycoplasma pneumonia (26%) and Influenza-B (19.8%). Coinfections were reported in 58% of samples and the most common association was found between B. pertussis and Adenovirus (12.2%). CONCLUSIONS: There was a high prevalence of Adenovirus, Mycoplasma pneumoniae and other etiologies in patients with a probable diagnosis of pertussis. Despite the presence of persistent cough lasting at least two weeks and other clinical characteristics highly suspicious of pertussis, secondary etiologies should be considered in children under 5 years-old in order to give a proper treatment.

Chlamydophila pneumoniae infection in patients undergoing carotid artery stent.

Although several reports have correlated Chlamydophila pneumoniae (CP) infection with carotid endarterectomy and coronary stent, no data have been reported on the potential relationship between this pathogen and carotid artery stenting (CAS). Hence, we evaluated 47 subjects, 27 symptomatic and 20 asymptomatic, before CAS intervention and during the follow up, for the presence of CP DNA and anti-CP antibodies, including chlamydial HSP60 (Cp-HSP60). Before stent placement, CP DNA was detected exclusively in symptomatic patients, all of whom were also positive for CP IgG and IgA and 85.7 percent of them also had CP-HSP60 antibodies. At the follow-up, all CP DNA positive and 11 out of the 13 symptomatic patients with Cp-HSP60 antibodies became negatives. In contrast, no change was observed for CP- IgA antibodies. Despite the small number of patients, the present study advocates an important role of CP infection in symptomatic patients with carotid artery disease. Our findings also suggest that stent placement and/or therapy might have a role in favouring resolution of inflammation, though not affecting persistence of CP infection.

Azithromycin does not prevent six-month myointimal proliferation but attenuates the transient systemic inflammation occurring after coronary stenting.

OBJECTIVES: Stent implantation produces a systemic increase of inflammatory markers that correlates with Chlamydophila pneumoniae infection in atherosclerotic plaque. We performed a clinical intervention study to investigate the effect of antibiotic treatment on 6-month follow-up angiographic minimal luminal diameter after stenting. METHODS: Ninety patients were randomly assigned to oral azithromycin or placebo in a double-blinded and randomized fashion. Medication was initiated 2 weeks before a pre-scheduled stenting procedure and maintained 12 weeks thereafter. Angiographic outcomes were evaluated by a six-month follow-up angiography and laboratorial parameters were accessed by blood sampling 2 weeks before stenting, within the first 24 h after procedure and additional samples after four weeks and 6 months. RESULTS: Minimal luminal diameter (1.76 +/- 0.56 mm Vs. 1.70 +/- 0.86 mm; P = 0.7), restenosis rate, diameter stenosis, late loss, and binary restenosis rates were comparable in placebo and azithromycin group in the 6 months follow-up. Serum levels of C-reactive protein presented a three fold significant increase in the control group one day after stenting but did not change in the azithromycin group (8.5 [3.0;16.4] Vs. 2.9 [1.7;6.6]-median [25;75 percentile] P < 0.01). CONCLUSIONS: Azithromycin does not improve late angiographic outcomes but attenuates the elevation of C-reactive protein levels after stenting, indicating an anti-inflammatory effect.

Exposure to Chlamydia pneumoniae infection and age-related macular degeneration: the Blue Mountains Eye Study.

PURPOSE: To assess cross-sectional and longitudinal associations between exposure to Chlamydia pneumoniae infection and age-related macular degeneration (AMD) in the nested case-control sample drawn from the Blue Mountains Eye Study (BMES) cohort. METHODS: The BMES examined 3654 persons aged 49 to 97 years during 1992 through 1994 (BMES I survey). Survivors from this cohort (n = 2335; 75%) and 1174 persons who moved in this area or reached an eligible age were examined during 1997 through 2000 (BMES II survey, n = 3509). One hundred ninety-seven AMD cases and 433 control subjects matched for age, sex and smoking status, were drawn from the BMES II survey. Photographic macular grading followed the Wisconsin grading system. Plasma samples were analyzed with an enzyme-linked immunosorbent assay to determine antibody titers to the elementary bodies from C. pneumoniae AR39. Associations between seroreactivity to C. pneumoniae and prevalent and incident AMD were assessed by using logistic regression models. RESULTS: There were 159 early and 38 late AMD cases. Of them, 87 cases of early and 22 of late AMD developed between the baseline and follow-up examinations. After adjustment for age, gender, and smoking, no significant association was evident between C. pneumoniae antibody titer and any prevalent early or late AMD (OR 1.02, 95% CI 0.66-1.56 comparing upper with lower tertile of antibody titer). Findings were similar when early or late AMD was analyzed separately. Analysis confined to incident AMD also showed no significant association with the incidence of either early (OR 0.92, 95% CI 0.52-1.64) or late (OR 1.85, 95% CI 0.57-6.05) AMD. The results did not change after adjustment for family history of AMD and cardiovascular disease. CONCLUSIONS: In this nested case-control sample of an older Australian population we found no association between C. pneumoniae antibody titers and early AMD. The study has insufficient power to assess an association with late AMD.

Usefulness of sparfloxacin against Chlamydia pneumoniae infection in patients with bronchial asthma.

The efficacy of sparfloxacin (SPFX) for the control of bronchial asthma was evaluated in 26 patients with suspected Chlamydia pneumoniae infection. Patients were randomly allocated to receive SPFX 200 mg/day (n = 14) or control treatment (n = 12) for 21 days. Significant improvements in serum C-reactive protein levels, and significant decreases in peripheral eosinophil counts, serum eosinophil cationic protein (ECP) and sputum ECP were observed in the SPFX-treated group at day 21. SPFX-treated patients also had a significantly reduced frequency of asthma symptoms, reduced inhalant beta2-stimulant use, and significant increases in morning peak expiratory flow. At the end of the study, C. pneumoniae was undetectable in two SPFX-treated patients who underwent polymerase chain reaction testing, but one control patient who was tested still had detectable levels of C. pneumoniae. These results suggest that SPFX could be used to control bronchial asthma in patients with suspected persistent C. pneumoniae infection.

Chlamydia pneumoniae infection after lung transplantation.

BACKGROUND: Chlamydia pneumoniae is established as a common agent of acute respiratory tract infection and has been implicated in the pathogenesis of asthma and chronic obstructive pulmonary disease. Airway disease is a prominent cause of morbidity and mortality after lung transplantation. We investigated the role of C pneumoniae as a pulmonary pathogen after lung transplantation. METHODS: Eighty lung transplant recipients underwent 232 bronchoscopies with bronchoalveolar lavage with or without transbronchial lung biopsy during 1 year for surveillance of rejection and infection, or where clinically indicated. RESULTS: C pneumoniae was detected using nested polymerase chain reaction in 9 of 36 (25%) recipients studied within 30 days of lung transplantation, 3 of whom remained positive on repeat lavage and died from airway disease in the first year post-operatively. By comparison, all 27 recipients with negative lavage survived >1 year. Lavage was positive for C pneumoniae in 18 of 71 (25%) recipients studied >30 days after lung transplantation, 5 of whom had pneumonia and 8 of whom had bronchiolitis obliterans syndrome. Eleven also had acute pulmonary allograft rejection. CONCLUSIONS: Persistent infection with C pneumoniae (whether donor-derived, de novo or re-activated) appears deleterious to pulmonary allograft function and is associated with early mortality, rejection and bronchiolitis obliterans syndrome after lung transplantation. A trial of empiric antibiotic therapy for C pneumoniae may therefore be warranted in the attempt to prevent progressive inflammatory airway disease.

Antimicrobial therapy in community-acquired pneumonia among emergency patients in a university hospital in Japan.

As antimicrobial therapy for pneumonia has not been well established in Japan, this study was designed to obtain a more definitive standard for antimicrobial treatment of this condition. Two hundred and thirty-one emergency patients admitted to Kyorin University Hospital between January 1998 and December 2000 were retrospectively analyzed in respect to their age, underlying disease, causative organism, and primary treatment with antimicrobial agent. Furthermore, the severity and prognosis were analyzed for those patients who had not responded to initial treatment with antimicrobial agents. The majority of the patients were elderly (over 65 years old; mean overall age 66.7 +/- 15.2 years) and had severe pneumonia; underlying diseases were recognized at a high rate in patients with severe pneumonia (P < 0.05) and in those classified as elderly (P < 0.0001). The most common underlying conditions in elderly patients were respiratory, cardiovascular (P < 0.01), and cerebrovascular (P < 0.05) diseases. The most common causative organisms were Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae, and Mycoplasma pneumoniae. In patients with severe pneumonia, S. aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa were identified as the most common causative organisms. Complications associated with antimicrobial treatment were observed in those patients with K. pneumoniae isolates who also had severe pneumonia and were frequently treated with penicillin. Furthermore, increased mortality rates were observed in patients not responding well to the initial treatment with antimicrobial agents. Thus, the selection of appropriate initial antimicrobial agents is an important factor affecting the prognosis of patients with community-acquired pneumonia.

[Significance of antibacterial therapy of Chlamydophila pneumoniae infection in patients with bronchial asthma]. / Znachenie antibakterial'noi terapii pri Chlamydophila pneumomiae infektsii u bol'nykh bronkhial'noi astmoi.

AIM: To study effects of eradication of Chlamydophila pneumoniae CP) infection in bronchial asthma (BA) on BA course and changes in quality of life (QOL) in BA patients. MATERIAL AND METHODS: 194 BA patients in clinical remission participated in the trial. Microbiological diagnosis of asymptomatic CP infection was made serologically (ELISA, indirect enzyme immunoassay) using polymerase chain reaction. Clinical and biochemical tests, assessment of pulmonary ventilation function, QOL by AQLQ during 6-week antimicrobial therapy were made in 56 patients. RESULTS: Patients with stable BA had high frequency of serological signs of clinically asymptomatic CP infection (52%) deteriorating BA symptoms and QOL. Antibacterial therapy of latent CP infection with azitromycin significantly improved BA course and QOL of BA patients. CONCLUSION: When laboratory tests detect CP infection in patients with long-term course of BA, especially in smoking males with moderate and severe BA it is clinically valid to prescribe addition of azitromycin to basic antiinflammatory treatment of BA.

High prevalence of Chlamydia pneumoniae infection in cyclosporin A-induced post-transplant gingival overgrowth tissue and evidence for the possibility of persistent infection despite short-term treatment with azithromycin.

BACKGROUND: Cyclosporin A (CsA) induces gingival overgrowth (GO) in up to a quarter of CsA-treated renal transplant recipients. A short-term therapy with azithromycin effectively reduces GO, indicating a possible involvement of microorganisms in the pathogenesis of CsA-induced GO. We aimed to determine if there could be any relationship between infection with Chlamydia pneumoniae and GO pathogenesis. In addition, we determined the long-term persistence rate of C. pneumoniae infection in residual GO tissue when azithromycin treatment failed to eliminate GO. METHODS: Chlamydia pneumoniae IgG and IgM antibody titres were measured by microimmunofluorescence technique in sera of kidney recipients with (n = 11) and without (n = 89) GO. GOs were rated and gingivectomies were performed before treatment with 500 mg of azithromycin for 3 days and at months 6 and 12 post-treatment when C. pneumoniae titres were re-evaluated. Nested polymerase chain reaction was performed to identify C. pneumoniae-specific DNA in GO tissues. Results of C. pneumoniae antibody titres from patients with GO were compared with pair-matched controls without GO. RESULTS: Chlamydia pneumoniae IgM titres were elevated in five of 11 patients with GO and in none without GO, whereas the difference of C. pneumoniae IgG titres between patients with GO and pair-matched controls did not reach significance (P<0.57). Chlamydia pneumoniae-specific DNA was found in 10 of 11 GO tissue samples pre-treatment. Azithromycin therapy effectively reduced GO and C. pneumoniae IgM titres. In residual GO, C. pneumoniae-specific DNA remained detectable after 1 year in all GO tissue samples despite azithromycin treatment. The C.pneumoniae IgM titres correlated with GO scores. CONCLUSION: Chlamydia pneumoniae infection is highly prevalent in CsA-induced GO. The infection can persist over a long period in residual GO despite short-term azithromycin therapy. The results indicate that CsA immunosuppression enhances C. pneumoniae infection rates in non-cardiovascular tissue.

Acute Chlamydia pneumoniae and Mycoplasma pneumoniae infections in community-acquired pneumonia and exacerbations of COPD or asthma: therapeutic considerations.

Rates of acute Chlamydia pneumoniae and Mycoplasma pneumoniae infections were determined in 115 adults hospitalized for community-acquired pneumonia (CAP), purulent exacerbations of COPD and acute exacerbations of bronchial asthma, by means of serology and molecular methods. Results were compared with those obtained in a matched control group. Common respiratory pathogens were isolated by cultures in 22.5% and 22.2% of CAP and exacerbated COPD patients, respectively. Cultures from exacerbated asthma patients were always negative. Serological and molecular evidence of current C. pneumoniae infection was obtained in 10.0%, 8.9% and 3.3% of CAP, COPD and asthma cases. The corresponding rates of acute M. pneumoniae infection were 17.5%, 6.7% and 3.3%, respectively. Finally, no difference was found between typical and atypical pathogen rates. These findings highlight the importance of taking into account C. pneumoniae and M. pneumoniae infections in guiding the choice of empirical antibacterial treatment for CAP and purulent exacerbations of COPD.

IFN-gamma induced persistent Chlamydia pneumoniae infection in HL and Mono Mac 6 cells: characterization by real-time quantitative PCR and culture.

Growth of Chlamydia pneumoniae during gamma interferon (IFN-gamma) induced persistent infection in epithelial (HL) and monocyte-macrophage (Mono Mac 6) cell lines was studied by a quantitative real-time PCR and passage. When HL cultures were treated with IFN-gamma (25 U/ml), the replication of C. pneumoniae DNA was unaffected while differentiation into infectious elementary bodies (EB) was strongly inhibited, and in contrast to the untreated cultures, no second cycle of infection was observed. The estimated doubling time of C. pneumoniae genomes was 6-7 h in both IFN-gamma treated and untreated HL cultures. At 72 h post inoculation, most infectious EBs were released from untreated cultures, whereas in IFN-gamma treated HL cells >90% of C. pneumoniae genomes were in non-infectious form. A higher dose (1000 U/ml) of IFN-gamma was needed to restrict growth of C. pneumoniae in Mono Mac 6 cells. In untreated Mono Mac 6 cultures, the growth curve of C. pneumoniae resembled that observed in HL cells, except that no second cycle of infection could be detected. In IFN-gamma treated Mono Mac 6 cultures, the number of infectious C. pneumoniae EBs recovered decreased gradually after 3 days post inoculation, while C. pneumoniae genome load remained unaltered suggesting persistence of C. pneumoniae also in these cells.

Severe Chlamydia pneumoniae infection in a patient with mild neutropenia during treatment of Hodgkin's disease.

Chlamydia pneumoniae is known to cause acute respiratory tract infections in the non-immunocompromised population. So far, no data about the incidence of chlamydial infections in neutropenic patients are available. Macrolide antibiotics are not considered to be first-line treatment options in neutropenic patients. We report the case of a patient with Hodgkin's disease who developed C. pneumoniae pneumonia during mild neutropenia. C. pneumoniae should be considered as a causative agent of pneumonia in neutropenic patients.

Chlamydia pneumoniae and acute chest syndrome in patients with sickle cell disease.

UNLABELLED: PURPOSE Few studies address the association of Chlamydia pneumoniae infection with pulmonary disease and outcome in patients with underlying pathology such as sickle cell disease (SCD). SCD patients are susceptible to the pulmonary disorder known as acute chest syndrome (ACS), where the etiology remains ill defined. The purpose of this study was to analyze the clinical course and outcome of C. pneumoniae-associated ACS among SCD patients as part of the National Acute Chest Syndrome Study. PATIENTS AND METHODS: This was a longitudinal study of SCD patients presenting with ACS to multiple U.S. medical centers. Two hundred ninety-six SCD patients who developed ACS were tested by PCR for C. pneumoniae and by standard techniques for other respiratory pathogens. These infections were evaluated for association with ACS, clinical course, and complications. RESULTS: Forty-one (14%) patients with first episodes of ACS were PCR positive for C. pneumoniae. Compared with other infections, C. pneumoniae-infected patients were older, were more likely to present with chest pain, and had higher hemoglobin levels at diagnosis. Both groups had similar rates of respiratory failure and prolonged hospitalization. Of the 89 patients with single-pathogen infections, 27 (30%) were due to C. pneumoniae, 21% to Mycoplasma pneumoniae, 10% to RSV, 4% to Staphylococcus aureus, and 3% to Streptococcus pneumoniae. CONCLUSIONS: C. pneumoniae was the most prevalent pathogen in this study of ACS and was responsible for significant morbidity. Additional research is required to develop effective treatment guidelines for ACS.

A casuistic immunologic response in primary and repeated Chlamydophila pneumoniae infections in an immunocompetent individual.

A casuistic immunologic response in primary and repeated Chlamydophila pneumoniae infection is described. The primary C pneumoniae infection was documented as laboratory accident in late 1990. The immunologic response was mediated mainly through production of IgM antibodies with only a marginal IgG and IgA increase near the cut-off value. The second episode of respiratory illness in the summer of 1999 that was clinically compatible with acute C. pneumoniae infection was characterised by only increase of specific IgM antibodies detected by microimmunofluorescence, EIA and Western blot analysis. Remarkably, in the first episode of C. pneumoniae infection IgM antibodies were predominantly to 60 kDA and LPS antigens, whereas in the second episode they were to a 40 kDA protein and LPS. Non-specific polyclonal B-cell activation by Epstein Barr virus infection as well as other possible common causes of acute respiratory illness were excluded by routine serology. Noteworthy, the patient was able to respond adequately to other pathogens (e.g. cytomegalovirus) as determined by IgG EIA. The reason for the observed uncommon immunological reaction remains enigmatic. However, quick therapeutic interventions (due to awareness) or massive infection load in the primary infection might have had some suppressive impact on the maturation of the immunity.

[Chlamydia pneumoniae and acute respiratory tract infections in breast-feeding infants: simultaneous mother-child serological study in Niamey (Niger)]. / Chlamydia pneumoniae et infections respiratoires aiguës chez l'enfant nourri au sein: étude sérologique simultanée mére-enfant à Niamey (Niger).

The age and the origin of Chlamydia pneumoniae primary infection in Sahelian areas are unknown. To evaluate the prevalence of C. pneumoniae antibodies, the authors studied the serological status of C. pneumoniae-, C. psittaci- and C. trachomatis-specific antibodies of 50 mother-child couples using the microimmunofluorescence technique. Children were 10 to 34 month-old (18,1 6,2, mean SD), breast-fed and hospitalized with acute respiratory tract infections in Niamey (republic of Niger). Specific C. pneumoniae IgG antibodies were present in 46/48 (95.8%) children, IgA in 32/48 (66.6%). In the mothers, specific C. pneumoniae IgG antibodies were present in 40/48 (83.3%), IgA in 31/48 (64.6%). The specific IgM antibodies were steadily absent in mothers and children. In the mother-child couples, 38/46 (79.2%) had specific C. pneumoniae IgG antibodies and 23/47 (48.9%) had IgA. The prevalence of specific C. pneumoniae IgG and IgA antibodies is very high in this population. These results point out that C. pneumoniae primary infection is very precocious in this paediatric population and is very different from American, Asian and European reports. A mother-child direct contamination during the first months of life in this breast-feeding pediatric population is discussed.

Elevated interleukin-6 predicts progressive carotid artery atherosclerosis in dialysis patients: association with Chlamydia pneumoniae seropositivity.

The cardiovascular mortality rate is unacceptably high in patients with end-stage renal disease (ESRD), which suggests an accelerated atherogenic process. The cause(s) of the accelerated atherogenesis in ESRD patients are not known, though recent studies suggest that persistent infection, such as Chlamydia pneumoniae, and proinflammatory cytokines may contribute. Forty-five ESRD patients (26 men) aged 51 +/- 2 years was studied at a time-point close to start of dialysis treatment and again after about 12 months of dialysis treatment. By using noninvasive B-mode ultrasonography, we evaluated changes in a surrogate marker of atherosclerosis, calculated intima media (cIM) area, in the common carotid artery. C-reactive protein (CRP), S-albumin, and interleukin-6 (IL-6) assessed the presence of an inflammatory reaction. We also measured C pneumoniae antibodies by microimmunofluorescence, nutritional status by subjective global assessment, lipid parameters, smoking habits, and the presence of comorbidity close to the start of dialysis. No significant changes in the prevalence of carotid plaques or the mean cIM area were observed during the first 12 months of dialysis. However, because some patients showed marked increases in the cIM area during only 12 months of dialysis we divided the patients into 2 groups: 23 nonprogressors ((delta)cIM area -2.7 +/- 0.4 mm2) and 22 progressors ((delta)cIM area 3.6 +/- 0.7 mm2). Sex, age, body mass index, comorbidity, blood lipid levels, S-albumin, and CRP levels did not differ significantly between the 2 groups. On the other hand, progressors had a significantly elevated basal median level of IL-6 (5.7 versus 3.1 pg/mL; P < 0.05) and an increased prevalence of positive (> or 1/64) immunoglobulin (Ig) A antichlamydia antibodies (59% versus 17%; P < 0.01) compared with nonprogressors. A significant positive (R = 0.41; P < 0.01) correlation was found between Log IL-6 and changes in the cIM area during 12 months of dialysis. In a stepwise multiple regression model, Log IL-6 did predict, independently (P < 0.01) of traditional risk factors and C pneumoniae antibodies, changes in the cIM area. These data suggest that a persistent chlamydial infection stimulates IL-6 levels, which in turn may be involved in the pathogenesis of accelerated carotid atherosclerosis in dialysis patients.

Detection of Chlamydophila pneumoniae in mouse respiratory ciliated epithelium using targeted sections of the lung tissue.

Chlamiophila pneumoniae were detected in targeted sections of mouse lung tissue by means of transmission electron microscopy and immunofluorescent staining. Incorporation of microorganisms into the axonemal matrix of cilia was observed 24 h after infection. The ciliary axoneme was characterized by pronounced swelling. At the late stages Chlamiophila pneumoniae were present in cytoplasmic vacuoles. Structural abnormalities and dysfunction of mucociliary clearance followed by incorporation of Chlamiophila pneumoniae into the cytoplasm of epitheliocytes were revealed in the early stage of infection. The proposed method allows studying the very early events of Chlamiophila pneumoniae infection.

Chlamydia pneumoniae infects and multiplies in lymphocytes in vitro.

The obligate intracellular pathogen Chlamydia (Chlamydophila) pneumoniae is known to be associated with some chronic inflammatory diseases, such as atherosclerosis. Interaction between C. pneumoniae and immune cells is important in the development of such diseases. However, susceptibility of immune cells, particularly lymphocytes, to C. pneumoniae infection has not been reported, even though lymphocytes play a pivotal role in the development of the diseases caused by this bacterium. In this regard, we examined the susceptibility of lymphocytes to C. pneumoniae infection in vitro. The results demonstrated that human peripheral blood lymphocytes as well as mouse spleen lymphocytes could be infected with C. pneumoniae. Furthermore, purified T lymphocytes as well as established T-lymphocyte cell line cells showed an obvious susceptibility to C. pneumoniae infection, indicating that T cells could be one of the host cells for this bacterial infection. These findings reveal a new infection site for C. pneumoniae, i.e., lymphocytes.

Indicators of infection with Chlamydia pneumoniae are associated with expansion of abdominal aortic aneurysms.

PURPOSE: Chlamydia Pneumoniae has been shown to be associated with atherosclerosis, myocardial infarction, and abdominal aortic aneurysms (AAAs). The possible association between AAA expansion and C pneumoniae infection was therefore assessed. METHODS: Blood samples were taken from patients with an AAA that was considered for surgical repair after having been diagnosed by means of the Chichester aneurysm screening program (UK) as having an initially infrarenal aortic diameter of 3.0 to 5.9 cm. The patients were examined prospectively for as long as 11.5 years (mean, 4.1 years) with ultrasound scanning. Of 110 patients considered for surgery, 90 men and 10 women had blood samples taken. Their IgG and IgA antibodies against C pneumoniae were measured by means of a microimmunofluorescence test. Unpaired t tests, multiple linear regression analyses, and logistic regression analyses were used for statistical analysis. RESULTS: A total of 44% (95% CI, 31%-55%) of the men with an AAA had an IgA titer of 64 or more, an IgG titer of 128 or more, or both, compared with 10% of the women with an AAA (OR = 7.2; 95% CI, 1.05-160.8). A titer of IgG of 128 or more was significantly associated with higher expansion (5.3 vs 2.6 mm per year), even after adjustment for initial AAA size and age. A significant positive correlation between both IgA and IgG titers and mean annual expansion was observed (r = 0.28; 95% CI, 0.05-0.49; and r = 0.45; 95% CI, 0.24-0.62, respectively), persisting after adjusting for initial AAA size and age. An IgG titer of 128 or more was present significantly more often in cases with an expansion greater than 1 cm annually (adjusted OR = 12.6; 95% CI, 1.37-293). CONCLUSION: A high proportion of men with an AAA has signs of infection with C pneumoniae. The progression of their AAAs was positively correlated with the presence of indicators of C pneumoniae infection.