Non-Bacterial Pneumonias

¹ Professor and Head, Department of Bacteriology and Immunology, University of Minnesota.

In recent years, evidence has accumulated of the successful application of present knowledge and of new developments in the field of diagnostic bacteriology and virology by the disentanglement with fair regularity of successive new entities from the "scrap pile" commonly referred to as "virus pneumonia," "interstitial pneumonia," "atypical pneumonia," or "non-bacterial pneumonia." Many factors are responsible for the disentanglement and recognition of successive etiologic entities from the complex. The process has been facilitated, a) by the ready availability and common employment of chemotherapeutic and antibiotic agents for treatment, thereby eliminating effectively most bacterial agents; b) by the increasingly frequent use of roentgenography for the study of any case of suspected pneumonia; c) by the realization in hospital practice that the need is for more, rather than less, precise bacteriologic diagnosis because of the specificity of antibacterial agents and the possibility through adaptation of the appearance of resistant bacteria; and d) by the development and application of new diagnostic laboratory methods.

This review of the non-bacterial pneumonias emphasizes:

1) The importance of the non-bacterial pneumonias as a component in the complex of pulmonary infection designated clinically and pathologically as pneumonia is of recent recognition. From five to 70 per cent of all pneumonias are non-bacterial.

2) The causative agents are known to include a wide variety of microbiologic agents and their products such as viruses, rickettsia, fungi, protozoa, toxins, and allergens.

3) The more usual pathological, roentgenological, and clinical pictures are essentially the same for this wide range of etiologic entities, but variable differences occur between successive cases of the same entity and of different entities.

4) Separation into etiological entities must be accomplished by laboratory studies.

5) The facilities available in many diagnostic laboratories are inadequate to cope with the problem of the isolation and specific identification of viruses. For this approach, a specialized laboratory, and, more particularly, specialized personnel are needed. Since the approach is simple and, in essence, that which is applied for the diagnosis of a bacterial disease, attempts should be made to establish a specific diagnosis by isolation of the virus from materials or tissues derived from the patient and by its identification or, when that is not possible, to establish the diagnosis in retrospect by assessing the patient's serum for specific antibodies.

6) The general recognition that such widely different biological agents as viruses, fungi, protozoa, and allergens may be the causative agents of non-bacterial pneumonia should stimulate the efforts of both the laboratorian and the clinician to direct their efforts toward making a specific diagnosis before antibiotic therapy is undertaken and not to be satisfied by nonspecific antibiotic "shot-gun" therapy.