Severe community-acquired pneumonia

Serum immunoglobulins in the infected and convalescent phases in community-acquired pneumonia

BACKGROUND

A population-based case-control study was designed to assess changes of serum levels of immunoglobulins and IgG subclasses between infected and convalescent phase in community-acquired pneumonia (CAP).

METHODS

Over a 2-year period, all subjects who were >14 years of age living in the Maresme region (Barcelona, Spain) diagnosed of CAP were registered. Controls were healthy subjects selected from the municipal census. Prognostic factors were assessed and serum levels of total IgG, IgA, IgM, and IgG subclasses were measured at diagnosis and 1 month later (cases).

RESULTS

We studied 171 patients with CAP and 90 controls. All immunoglobulins were significantly lower in cases than in controls. At diagnosis, 42.7% of cases showed low levels of some immunologic parameter, mainly total IgG and IgG2. Low immunoglobulin levels at diagnosis were more frequent in patients requiring in-patient care and in those with pneumonia of other etiology than Streptococcus pneumoniae. In the convalescent phase, 26 (23.6%) patients normalized immunological levels. In 27 (24.5%) cases, some parameter with low levels persisted especially in patients with etiology of CAP other than S. pneumoniae.

CONCLUSIONS

Low serum levels of immunoglobulins particularly total IgG and IgG2 were a common finding in patients with CAP compared to healthy controls. Low immunoglobulin levels may be related to CAP prognosis and persisted in the convalescent phase in one-fourth of cases.

Diagnosis of pneumonia and monitoring of infection eradication

Pneumonia can be classified as community-acquired (CAP) or hospital-acquired (nosocomial). Both are frequent infections that demand a great amount of medical resources. The diagnosis of CAP is based on clinical signs and the presence of a pulmonary infiltrate visible on chest radiograph. For practical purposes, CAP has been classified as typical, with an acute onset in which the most representative microorganism is Streptococccus pneumoniae, and atypical, with a subacute onset (Mycoplasma pneumoniae). Nevertheless, so far no studies have clearly demonstrated the utility of this classification in predicting the aetiology. Guidelines on CAP recommend associating the aetiology of CAP with comorbidity, age and severity. The microbiological diagnosis relies mainly on Gram stain and sputum culture, but this technique has disadvantages such as frequent contamination of the sample with oropharyngeal commensal flora, frequent sterile cultures associated with previous antibiotic treatment, and the fact that approximately 40% of patients are not able to expectorate. Other diagnostic techniques such as blood cultures, serological tests and fibreoptic bronchoscopy must be reserved for patients who are hospitalised, especially if they need admission to an intensive care unit. Compared with CAP, nosocomial pneumonia has major diagnostic problems due to the presence of other diseases able to mimic pneumonia and frequent bacterial colonisation of the lower respiratory tract. Most of the diagnostic techniques produce a high percentage of false-negative and false-positive results. This is especially true for ventilator-associated pneumonia. There is controversy over using a comprehensive aetiological work-up based on bronchoscopic techniques or only on quantitative culture of endotracheal aspiration. By contrast, there is consensus about the importance of the adequacy of empirical antibiotic treatment, since mortality rates are higher in patients who are inadequately treated. Once treatment of pneumonia has begun, it must be maintained for 48 to 72 hours because this is the minimum time to evaluate a clinical response. Antibacterial agents have to be adjusted according to microbiological findings. In nonresponding patients, pneumonia-related complications and the presence of multiresistant micro-organisms or non-covered pathogens must be ruled out.