Daijiworld Media Network - Washington

Washington, Dec 11: A 35-year analysis from the United States has underscored the urgent need for thorough and timely antemortem testing to accurately detect human rabies—an infection that often goes undiagnosed before death due to limited sampling and delayed testing.

The study evaluated 69 confirmed human rabies cases reported to the U.S. Centers for Disease Control and Prevention (CDC) between 1990 and 2024. Each case included at least one antemortem sample, such as saliva, nuchal skin biopsy, serum, or cerebrospinal fluid (CSF). In total, 382 samples were examined under standard diagnostic protocols.

Researchers assessed the diagnostic sensitivity of each sample type and examined how the probability of detection changed across the course of the illness. The timeline revealed a narrow diagnostic window:

• Median time to first positive sample: 8 days from symptom onset

• Median time to death: 16 days

These findings highlight the challenges clinicians face in confirming rabies while patients are still alive.

When clinicians collected all four recommended sample types, the combined diagnostic sensitivity reached 100%, with the risk of a false-negative result dropping to below 2%.

However, testing only one sample type drastically reduced sensitivity to below 65%, posing a significant risk of missed diagnosis.

The analysis also revealed timing-specific detection patterns:

• Saliva and nuchal skin samples were more likely to detect the virus early in the illness.

• Serum and CSF antibody tests were more effective later, reflecting the body’s evolving immune response.

Experts stress that negative results—especially from a single early sample—cannot rule out infection. In suspected cases of rabies or rabies encephalitis, clinicians must follow CDC guidelines to collect all four sample types at multiple points in the illness. This approach ensures maximum diagnostic accuracy and supports critical decisions related to patient management, infection control, and public health response.

The study concludes that understanding how sensitivity varies by sample type and timing is essential for interpreting results and improving detection of one of the world’s deadliest yet often underdiagnosed infections.