Acute Chlamydia pneumoniae infections in asthmatic and non-asthmatic military conscripts during a non-epidemic period
Abstract
Chlamydia pneumoniae respiratory tract infections were studied in 512 male military conscripts (123 asthmatic and 389 non-asthmatic) taking part in 180-day service between July 2004 and July 2005 in Kajaani, Finland. Respiratory tract infections requiring a medical consultation were analysed prospectively. At baseline, at end of service, and during each episode of respiratory infection, blood samples were obtained for measurement of C. pneumoniae antibodies. Data concerning the clinical features of each infection episode were collected. Serological evidence of acute C. pneumoniae infection was found in 34 of the 512 conscripts with antibody data available, including 9.8% of the asthmatic subjects and 5.7% of the non-asthmatic subjects (p 0.111). A serological diagnosis could be made for 25 clinical episodes in 24 conscripts. The spectrum of respiratory tract infections included 13 episodes of mild upper respiratory tract infection and seven episodes of sinusitis, with five episodes involving asthma exacerbation. Two of three pneumonias were primary infections. Primary infections were diagnosed in five subjects, and re-infection/reactivation in 19 subjects, with the latter comprising 12 non-asthmatic subjects and seven asthmatic subjects (p 0.180). Prolonged infections were present in six asthmatic subjects and one non-asthmatic subject (p 0.001). A wide variety of respiratory tract infections, ranging from common cold to pneumonia, were associated with serologically confirmed C. pneumoniae infections. Infections were often mild, with common cold and sinusitis being the most common manifestations. Acute, rapidly resolved C. pneumoniae infections were equally common among asthmatic subjects and non-asthmatic subjects, whereas prolonged infections were more common among subjects with asthma.
Introduction
Chlamydia pneumoniae has been associated with both epidemic and endemic episodes of acute respiratory disease [1]. Primary C. pneumoniae infections occur mostly in children, particularly school children [2,3], and the majority of adults show serological evidence of past infection [4]. Recurrent or secondary respiratory tract infection can occur, even when antibodies induced by a previous infection are still detectable in serum [5]. A particular feature of C. pneumoniae is its ability to cause prolonged or chronic infection. Serology, based on the use of paired sera, is the tool used most often for the routine diagnosis of acute C. pneumoniae infections [5,6], although this approach is only useful retrospectively.
C. pneumoniae can cause both upper and lower respiratory tract infection. Mild and asymptomatic infections are characteristic of C. pneumoniae [7,8], and typical infections are also characterised by gradual onset, pharyngitis with hoarseness, mild cough and transient fever. The disease may have a biphasic course, with resolution of pharyngitis before the development of bronchitis or pneumonia [1,2,4,9,10]. Cough is very common and often prolonged. Central nervous system symptoms, including headache, also seem to be common in patients with C. pneumoniae pneumonia [11].
The role of C. pneumoniae in acute bronchitis and pneumonia is well-established. Pneumonia caused by C. pneumoniae does not differ clinically from pneumonia caused by other common respiratory tract pathogens [11,12], and mixed infections with other respiratory pathogens, mainly Streptococcus pneumoniae, have also been reported [13]. As a causative agent of acute pharyngitis [14], C. pneumoniae seems to be mainly a co-pathogen rather than a primary agent [15]. Symptoms of sinus infection commonly occur in connection with C. pneumoniae infections, and the organism has been isolated from patients with purulent sinusitis and otitis media with effusion [4]. In addition, several chronic inflammatory diseases have been associated with C. pneumoniae infection, including cardiovascular disease, chronic obstructive pulmonary disease and asthma [16,17]. C. pneumoniae infection has been associated with the pathogenesis of both stable asthma and asthma exacerbations [18].
The aim of the present study was to investigate respiratory tract infections caused by C. pneumoniae in young asthmatic men and non-asthmatic men who required a medical consultation during their 180-day military service period in Kainuu Brigade, Kajaani, Finland. Data concerning episodes of respiratory tract infection were collected from a group of 235 military conscripts between July and December 2004, and from a second group of 283 conscripts between January and June 2005.
Materials and methods
Study subjects
In total, 892 men from two intake groups entering compulsory military service in July 2004 and January 2005, respectively, in Kajaani Garrison, northern Finland were eligible for recruitment to the study and signed an informed consent form allowing the use of their data for scientific purposes. All men with medically diagnosed asthma, together with randomly chosen men without asthma, were asked to participate. Of the total of 892 subjects, 518 were included in the present study based on the length of their service (180 days); these comprised 235 (64 asthmatic) men in the July 2004 intake group and 283 (60 asthmatic) men in the January 2005 intake group. The remaining 374 men with 270- or 360-day periods of service were partly trained in other units. Six of the 518 men lacked data concerning C. pneumoniae antibodies, and these subjects were subsequently excluded.
At the beginning of their military service, each conscript was asked to fill in a questionnaire concerning his atopy/allergies, previous respiratory tract infections and tobacco smoking habits. Blood samples were collected at the beginning and end of service, and in the acute and convalescent phases of each infection episode. Conscripts were accommodated during their service in barrack rooms for eight to ten individuals. The study protocol was approved by the Ethics Committee of Kainuu Central Hospital.
Asthma
A questionnaire was used to obtain information concerning medically diagnosed asthma; this is the most commonly used and validated method [19]. It was also possible to analyse self-reported data concerning previous health examinations by a physician.
Tobacco smoking
Smoking habits were classified on the basis of three questions: (i) ‘have you ever smoked?’; (ii) ‘do you smoke daily (cigarettes, cigars or pipe)?’; and (iii) ‘how much do you currently smoke daily or did you smoke before cessation, i.e., how many cigarettes per day?’ Current smokers were defined as those who smoked daily, while non-smokers had never smoked, or had quit smoking, or smoked only occasionally. The cumulative lifetime consumption of cigarettes was determined in terms of pack-years (the number of cigarettes per day × the number of years/20).
Respiratory tract illness
Conscripts with acute or acutely aggravated respiratory tract symptoms were checked by a nurse and examined by a physician, if necessary, in the military primary-care clinic in Kainuu Brigade. The episode was included in the database if a respiratory tract infection or an exacerbation of asthma was diagnosed by the physician. The diagnosis of respiratory tract infection was based on symptoms and clinical findings. Bacterial infections were diagnosed according to the recommendations of the Finnish National Guidelines [20]. If necessary, sinus ultrasound, sinus and chest radiography, blood tests (C-reactive protein (CRP) and leukocytes) and throat swabs for bacterial culture were used to help the clinician differentiate between viral and bacterial infections. Asthma exacerbation was defined as an increase in asthma symptoms (cough, breathlessness) or an increase in bronchodilator use and/or a reduced peak expiratory flow rate and/or wheezing on clinical examination. Mild episodes not referred to a physician were not included in the analyses. Further consultations within a 2-week period were considered as a single episode. Symptoms, clinical findings and drug prescriptions were recorded. Respiratory tract diseases were categorised as common cold, otitis, tonsillitis, sinusitis, bronchitis, pneumonia or exacerbation of asthma.
C. pneumoniae serology and CRP determination
Sera were collected from all participants at the beginning and end of service. In addition, acute and convalescent serum samples were collected during respiratory tract infections for the measurement of CRP and C. pneumoniae antibodies. The samples were stored at −80°C until analysed. The sera were tested for IgG, IgA and IgM antibodies to C. pneumoniae by the microimmunofluorescence test, using purified elementary bodies of Kajaani 6 as described previously [21,22]. All the sera from a particular subject were tested in the same series to minimise inter-assay variation. Four-fold serum dilutions were used, starting from 1:32 for IgG and 1:10 for IgA and IgM. The serum dilutions were incubated in a moisturised chamber for 1 h at 37°C for IgG, overnight at 8°C for IgA, and for 3 h at 37°C for IgM. IgA- and IgM-positive sera were retested after treatment with Gullsorb reagent (Gull Laboratories, Salt Lake City, UT, USA) to avoid false-positive reactions [23,24]. The presence of IgM antibodies in titres of ≥10 after Gullsorb treatment was used to define evidence of primary infection, and seroconversions suggesting acute infection were based on a four-fold rise in IgG and/or IgA titres between consecutive sera. Prolonged C. pneumoniae infections were defined on the basis of an elevation period of ≥2 months following an acute rise in titre.
CRP concentrations were measured by enzyme immunoassay (IBL Immunobiological Laboratories, Hamburg, Germany) according to the manufacturer’s instructions [25]. The CRP concentration in serum was determined by interpolation from a standard curve constructed from CRP standard solutions of 0–100 mg/L. The minimum detection limit of the test was 1 mg/L.
Statistical methods
Statistical analyses were performed using SPSS v.13.0 (SPSS Inc., Chicago, IL, USA). Age comparison was performed using Student’s t-test. Categorical variables were compared using chi-squared or Fisher’s exact tests, as appropriate.
Results
A recent C. pneumoniae infection was diagnosed serologically in 34 (6.6%) of the 512 conscripts. The characteristics of these 34 men are shown in Table 1 in comparison with the characteristics of all 512 conscripts included in the study. Twenty-two of the men with recent C. pneumoniae infection were non-asthmatic and 12 were asthmatic, with no significant difference between the non-asthmatic and asthmatic groups (5.7% vs. 9.8%, p 0.111).
| Entire study population | Conscripts with recent C. pneumoniae infection | |||||
|---|---|---|---|---|---|---|
| Total | July 2004 | January 2005 | p | July 2004 | January 2005 | |
| Subjects, n | 512 | 231 | 281 | 10 | 24 | |
| Age, years, mean (SD) | 19.6 (0.7) | 19.6 (0.8) | 19.6 (0.6) | 0.549a | 19.4 (0.9) | 19.5 (0.4) |
| Asthmatic, n (%) | 123 (24.0) | 63 (27.3) | 60 (21.4) | 0.119b | 4 (40.0) | 8 (33.3) |
| Current smoker, n (%) | 226 (44.8) | 95 (41.7) | 131 (47.5) | 0.193b | 4 (40.0) | 9 (37.5) |
- aStudent’s t-test.
- bChi-squared test.
Acute primary infections with the presence of IgM titres of ≥10 were seen in 13 men, nine without and four with asthma. In five men, IgM antibodies were present at the beginning of service, suggesting scars from a previous infection, and another five men had IgM antibodies in sera taken at the end of service, but these ten men had no clinical illness. A clinical illness was diagnosed in the other three men with IgM titres ≥10. In addition, acute primary infection with clinical illness was diagnosed in two conscripts on the basis of the IgG antibody response, as no IgG antibodies were present in the acute phase.
Acute re-infections or reactivations of chronic infection, with a four-fold or greater rise in IgG antibodies, were found in 19 conscripts, including 12 (3.1%) of the 389 non-asthmatic men and seven (5.7%) of the 123 asthmatic men (p 0.18) (one with two episodes), and all of these subjects had a clinical illness. Primary infections were diagnosed in five men, three in non-asthmatic men and two in asthmatic men. Prolonged infections were diagnosed in one (0.3%) of 389 non-asthmatic men and in six (4.9%) of 123 asthmatic men (p 0.001).
The clinical picture was compatible in 24 men (one with two episodes) with laboratory-confirmed C. pneumoniae infection. The clinical symptoms and the diagnoses of these 25 episodes are shown in Tables 2 and 3. Sixteen of the clinical episodes occurred during the winter season between September 2004 and April 2005, ten in the July 2004 intake group, and 24 in the January 2005 intake group. Body temperature was <38°C in 22 and >38°C in three infectious episodes. CRP was ≤10 mg/L in nine, 10–50 mg/L in 12 and >50 mg/L in four episodes. Three men with upper respiratory tract infection and two men with sinusitis also experienced exacerbation of asthma. Three cases of pneumonia were diagnosed, two of which were primary infections. Antimicrobial agents were prescribed for 12 episodes, including the three men with pneumonia who were prescribed roxithromycin for 14 days. Men with prolonged infection were treated for common cold and sinusitis. The following antimicrobial agents were prescribed for sinusitis: amoxycillin, amoxycillin–clavulanate and trimethoprim–sulphamethoxazole.
| Symptom | No. (%) of episodesa |
|---|---|
| Cough | 20 (80) |
| Rhinitis | 17 (68) |
| Fever | 14 (56) |
| Sore throat | 12 (48) |
| Headache | 6 (24) |
| Dyspnoea | 5 (20) |
| Earache | 3 (12) |
| Hoarseness | 2 (8) |
| Sputum | 1 (4) |
| Chest soreness | 1 (4) |
| Myalgia | 1 (4) |
| Eczema | 1 (4) |
- aOne episode could have more than one associated symptom.
| Clinical diagnosis | No. (%) of episodesa |
|---|---|
| Common cold | 13 (52) |
| Sinusitis | 7 (28) |
| Tonsillitis | 5 (20) |
| Exacerbation of asthma | 5 (20) |
| Pneumonia | 3 (12) |
| Bronchitis | 3 (12) |
| Otitis media | 1 (12) |
- aOne episode could have more than one associated diagnosis.
Discussion
The clinical picture of C. pneumoniae infection has been studied primarily during epidemic periods [1,26–29]. The present study period (July 2004 to July 2005) can be considered to be a non-epidemic period with respect to C. pneumoniae infections in Finland. The number of laboratory-confirmed C. pneumoniae infections in Finland has varied from 90 to 430 cases annually during the past decade, being highest in 2003 and lowest in 2006. In 2004, 245 C. pneumoniae infections were registered in Finland, and 32.2% (79/245) of these infections occurred between June and December (National Public Health Institute, unpublished data). In 2005, 113 infections were registered, 62.8% of which occurred between January and July. Usually, >50% of C. pneumoniae infections occur in Finland during winter. In the present study, 16 (47.1%) of the clinical episodes occurred between September 2004 and April 2005.
Primary infections occur mostly during childhood. In the present study, primary clinical illnesses were diagnosed in five (14.7%) young men. A four-fold rise in C. pneumoniae IgG antibodies, suggesting re-infection or reactivation of a persistent infection, was naturally more common, being confirmed in 19 men (one with two episodes). Since C. pneumoniae, like other Chlamydia spp., tends to cause persistent infection, serological tests do not differentiate between re-infections and reactivation of chronic infection during acute episodes in adults. C. pneumoniae infections during epidemics may involve a combination of both primary and secondary infections, and further molecular or typing investigations are required to determine whether a strain represents a reactivated strain or a new infection.
C. pneumoniae has been associated with asthma in various ways; an infection may precede the onset of asthma, exacerbate asthma or make the management of asthma more difficult [30]. The present data revealed no statistical difference in the number of serological diagnoses of recent C. pneumoniae infections, or in the number of C. pneumoniae re-infections or reactivation episodes, between asthmatic men and non-asthmatic men, but prolonged clinical infection with persistently elevated IgG antibodies after an acute C. pneumoniae episode was diagnosed in six asthmatic men and one non-asthmatic man (4.9% vs. 0.3%, p 0.001). However, the number of prolonged infections was small, and further research is required to confirm the suggestion that asthmatic individuals are prone to prolonged C. pneumoniae infection, although similar findings have been published previously [31].
As reported previously, non-productive cough is a common symptom, and fever is of low grade [32]. In the present study, most infections were mild, with fever of <38°C in 22 episodes and CRP values of <50 mg/L in 21 episodes. It has been estimated that c. 70% of all C. pneumoniae infections are asymptomatic [8]. In the present study, asymptomatic infections were evidently present in five men with IgM titres of ≥10 at the end of their service. These individuals may have had actual subclinical disease, or may have been so eager to complete their service that they ignored their symptoms.
Pneumonia and bronchitis are the most frequently recognised clinical illnesses associated with C. pneumoniae, although asymptomatic or mildly symptomatic illness is the most common feature of infection [4]. In the present study, 13 of 25 C. pneumoniae infections were diagnosed as upper respiratory tract infections, with the next most common diagnosis being sinusitis (seven cases). Pneumonia and bronchitis were both diagnosed in three subjects. According to previous studies, 5% of cases of bronchitis and sinusitis in adults are associated with C. pneumoniae infection [4], and this organism has been isolated from patients with purulent sinusitis and from patients with otitis media with effusion [33]. It has also been suggested previously that more than one apparent aetiological agent can be demonstrated in a majority of cases of C. pneumoniae pneumonia [10]. Evidently, acute or chronic infections caused by intracellular pathogens such as C. pneumoniae may pave the way for invasion by other bacteria, e.g., S. pneumoniae [13] and Haemophilus influenzae [12], and some of the patients in the present study, e.g., those with sinusitis, might have been affected by a combination of various aetiological agents.
In the majority of respiratory tract infections, the aetiological diagnosis remains obscure and empirical antibiotic therapy is prescribed. Coverage against atypical pathogens should be provided for community-acquired pneumonias. Macrolides, tetracyclines, ketolides and fluoroquinoles demonstrate both in-vitro and in-vivo activity against C. pneumoniae [34], but this organism is not treatable with penicillin, ampicillin and sulphonamides. In the present study, men with pneumonia were treated with roxithromycin, but those with prolonged infection and sinusitis were prescribed antimicrobial agents according to the recommendations for sinusitis [35], none of which provide coverage against C. pneumoniae. It is possible that these men could have recovered sooner with antibiotics effective against C. pneumoniae, but the use of antimicrobial agents poses a risk for the development of antibiotic resistance, particularly with respect to macrolide resistance among S. pneumoniae [36]. The current treatment guidelines should be followed, but additional coverage against C. pneumoniae should be provided in the case of prolonged infection.
In conclusion, during a non-epidemic period, C. pneumoniae infections among adolescents are mostly mild upper respiratory tract infections, but the full range of clinical respiratory infections can appear. Recent C. pneumoniae infections, including episodes of re-infection or reactivation, are equally frequent among asthmatic men and non-asthmatic men, while prolonged infections with persistent symptoms and elevated IgG levels seem to be more common among men with asthma than in those without asthma (p 0.001). Further research concerning this discrepancy during an epidemic period would be of interest.
Acknowledgements
This study was supported by Finnish Defence Forces and the Scientific Advisory Board for Defence. The authors declare that they do not have any commercial interests in relation to this study.
