Daijiworld Media Network - Washington

Washington, Dec 10: A 35-year U.S. analysis has found that human rabies often goes undetected because patients are not consistently tested before death and, when they are, limited sampling reduces the chances of confirming infection. The study emphasises that collecting all four recommended antemortem sample types—saliva, nuchal skin, serum and cerebrospinal fluid—across the course of illness is crucial for accurate diagnosis.

The investigation reviewed 69 confirmed human rabies cases reported to the U.S. Centers for Disease Control and Prevention (CDC) between 1990 and 2024. A total of 382 antemortem samples were analysed, and diagnostic performance was assessed based on sample type and timing. The median time from symptom onset to the first positive result was 8 days, while the median time to death was 16 days, highlighting a narrow window for clinical and public health intervention.

Key findings showed that when all four sample types were collected, diagnostic sensitivity reached 100 percent, with false negatives dropping to under 2 percent. However, relying on just one sample type reduced sensitivity to below 65 percent, significantly increasing the risk of missed diagnoses. Virus detection in saliva and nuchal skin tended to occur earlier in illness, while antibody detection in serum and cerebrospinal fluid increased later as the immune response evolved.

The study underscores the importance of strategic sample collection and timing when evaluating suspected rabies or rabies encephalitis. A negative result from a single early sample cannot rule out infection unless all recommended specimens are obtained. Investigators stress the need for clinicians to align with CDC guidelines to maximise diagnostic accuracy and ensure timely patient management, infection control and public health response.

Understanding how diagnostic sensitivity shifts across different sample types and days from symptom onset, the researchers noted, remains central to interpreting antemortem human rabies testing results.