One of my general principles when treating and diagnosing infectious diseases is to try and pursue a cause as far as I can. With a specific cause, one can discontinue treatments that were being used to cover all possibilities and provide as specific targeted therapy as is available. In addition to immediate treatment related implications there are others that, while not changing treatment (a mantra I hear all too often), are vitally important: infection control and epidemiologic intelligence.
When a hospitalized person with pneumonia is diagnosed with a specific virus such as, for example, parainfluenza virus for which there is not a specific antiviral treatment several things happen which include discontinuation of antibiotics (hopefully) and placement of the patient in droplet isolation to prevent contagion. However, if the specific diagnosis is not made the patient will languish on the floor marinating in antibiotics while coughing the virus onto his roommate and others.
A recent news story from a suburban Pittsburgh newspaper highlights the other important aspect of specific diagnoses: epidemiologic intelligence. The piece details a 74% uptick in the number of pneumonia cases in young adults diagnosed in a chain of urgent care centers in the area. This cluster of illnesses is important and interesting as influenza season really hasn't fully commenced in the region. However, what strikes me about this episode is that there seems to be no effort to understand which microbe is behind the cases: is it parainfluenza, an adenovirus, mycoplasma, RSV, a rhinovirus, a coronaviruses, legionella, pneumococci or some combination of different viruses and bacteria? Unfortunately, that is something that urgent care centers not associated with hospitals tend never to pursue because "it doesn't change patient care" despite the fact that it could have crucial epidemiologic importance. In many ways urgent care centers are places where symptomatic treatment without regard to causation is the norm and expected treatment paradigm.
What if these undiagnosed cases contain new microbes making their first forays into humans? What if there are important changes in viral prevalence occurring? We probably won't know because no diagnostic tests were likely done. Also, a good proportion of those cases are likely viral in nature but invariably were given a "Z-pack" nonetheless or potentially harmful steroids.
To me exploring these syndromes to identify the cause is what the specialty of infectious diseases is about. To me, in 2017, when there are multiple diagnostic tools in relatively easy reach in the US ranging from point-of-care influenza molecular diagnostic tests to multiple pathogen assays (also point of care) that there really should be no barrier to ordering these tests, especially at urgent care centers where patients are insured.
The diagnostic black hole in infectious disease in developed countries really baffling to me and makes no sense given that microbes have no borders. Recall that the 2009 H1N1 influenza virus emerged in Mexico and was first recognized in San Diego in a patient with mild symptoms who happened to have a diagnostic test that "doesn't change treatment" ordered.
The diagnostic test you order or fail to order may be more consequential than you think.