| Clinical Features |
Critical illness or death from a potentially infectious cause occurring in previously healthy persons. No aetiology identified on initial testing. |
| Etiologic Agents |
Multiple. Results of primary and secondary testing provided evidence of presumed etiologies in 28% of cases including disease due to the following pathogens: Streptococcus pneumoniae (15), Influenza A/B viruses (11), Mycoplasma pneumoniae (8), Neisseria meningitidis (7), Group A Streptococcus (5), Enterovirus (5), Chlamydia pneumoniae (4), Adenovirus (3), Legionella spp. (3), Bartonella spp. (3). |
| Incidence |
At least 0.5 cases per 100,000 persons 1-49 years of age. Most common clinical syndromes are central nervous system (meningitis, encephalitis) (26%), respiratory (33%), cardiac (16%), sepsis/multiorgan failure (14%), hepatic (4%). |
| Sequelae |
Overall, 62% of cases are fatal; of these, 79% had autopsies. |
| Transmission |
Varied. Unknown mode of transmission for unexplained cases. |
| Risk Groups |
General population. |
| Surveillance |
Active population-based surveillance through coroners and medical examiners in four Emerging Infections Programme (EIP) sites with total population of 6.7 million 1-39 year olds. Active institution-based surveillance for severe pneumonia is conducted at selected EIP sites. National and international surveillance is passive for clusters of unexplained deaths and illnesses. |
| Trends |
Efforts to more readily identify emerging pathogens will depend on both advances in diagnostic tests and modifications in public health surveillance. Bioterrorism preparedness requires the capacity to detect and evaluate cases or clusters of unexplained deaths or critical illnesses. |
| Challenges |
Simplify the case-finding methods; improve collaboration between clinicians, pathologists and public health practitioners; enhance the quality of clinical specimens available for testing; systematically evaluate role and utility of new techniques for identifying infectious pathogens. |
| Opportunities |
Build an infrastructure to evaluate cases of unexplained infectious disease; respond to clusters of unexplained illness in the United States and abroad; detect emerging pathogens or possible acts of biologic terrorism by challenging the limits of our diagnostic capabilities. |
