That the fatal cluster of respiratory illnesses in Texas is due to influenza doesn't come as a surprise. What is surprising is how such a cluster is headline grabbing.
The poor ability to diagnose influenza is what causes clusters like this to fuel speculation regarding novel pathogens that might be responsible. However, perusing any tertiary care center's ICU one will undoubtedly be able to find some sort of cluster of unexplained severe pneumonia patients.
Why are definitive microbiologic diagnoses elusive?
An ordinary pneumonia patient admitted to the ICU might have the following two microbiologic tests performed:
- Blood cultures: only positive in 5-14% of cases
- Sputum gram stain and culture: only 40% of patients are able to produce sputum
Other tests that are variably performed include pneumococcal and legionella urinary antigen testing. Rapid influenza and RSV antigen testing, notably unreliable but helpful if positive, may also be done. PCR testing for multiple respiratory viruses, including influenza, is unfortunately the most rarely done, often relegated exclusively to tertiary care centers.
In sum, the majority of pneumonia patients undergo a minimal amount of testing leaving the great majority of patients without an identified pathogen--a great number of which are likely viral in nature. To minimize unexplained clusters of illness, diminish the amount of unnecessary antibiotic use, improve infection control (as respiratory viral infections merit contact and droplet precautions), and identify influenza cases that will benefit from antiviral therapy, it is our diagnostic capacity that must improve.