TABLE 1—

Study Inclusion and Exclusion Criteria

Inclusion Criteria	Exclusion Criteria
Aged 1–49 years	At least 1 of the following ICD-9-CM codes delineated by Perkins et al.6: 042–044.9 and 795.8 (HIV disease), 140–239.9 (neoplasms), 250.0–250.9 (diabetes mellitus), 279.0–279.9 (disorders of the immune mechanism), 295.5 (other diseases of the spleen), 800–999 (injuries and poisonings)
Admitted to an intensive care unit, August 1996–December 1996
New Haven County resident
Exhibited infectious symptomatology or signs, including fever, rash, sepsis, shock, blood in sputum, chills, cough, diarrhea, ear pain or discharge, excessive sweating, headache, sinus congestion, sore throat	Underlying conditions, including chronic alcohol disease, chronic cardiac disease, chronic lung disease, immunosuppression, kidney disease, liver disease, rheumatologic disease
At least 1 of 84 ICD-9-CM codes
77 codes delineated by Perkins et al.6
7 codes determined to be possible indicators of unexplained illness and death by the authors: 345.3 (seizure, grand mal status), 426.0 (atrioventricular block, complete), 427.4 (ventricular tachycardia), 427.5 (cardiac arrest), 429.0 (myocarditis, no organism specified), 429.9 (heart disease, unspecified), 436.0 (acute, ill-defined cerebrovascular disease)

Note. ICD-9-CM = International Classification of Diseases, Ninth Revision, Clinical Modification