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Volume 10, Number 8—August 2004

Research

Acute Encephalitis Hospitalizations, California, 1990–1999: Unrecognized Arboviral Encephalitis?

Rosalie T. Trevejo*Comments to Author 
Author affiliation: *Western University, Pomona, California, USA

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Table 3

Diagnoses and month of admission for patients hospitalized with acute infectious or unspecified encephalitis in selected California counties, 1991–1999

Sacramento-Yolo Sutter-Yuba Imperial- Riverside
1995 Population estimates
1,271,500
135,400
1,500,300
Diagnosis (ICD-9-CMa)
No. of encephalitis diagnoses (%)b
Encephalitis of unspecified cause
305 (60.2)
45 (70.3)
338 (58.2)
Viral encephalitis with specified cause, not arboviral
74 (14.6)
11 (17.2)
112 (19.4)
Other causes of encephalitis
76 (15.0)
5 (7.8)
64 (11.1)
Postinfectious causes of encephalitis
38 (7.5)
1 (1.6)
45 (7.8)
Bacterial/rickettsial causes of encephalitis
10 (2.0)
0 (0)
7 (1.2)
Parasitic/protozoal causes of encephalitis
2 (0.4)
1 (1.6)
5 (0.09)
Arthropodborne viral encephalitisc
2 (0.4)
1 (1.6)
7 (1.2)
Total no. of encephalitis diagnosesd
507
64
578
Month of hospital admission
No. of admissions (%)
January–March
112 (22.1)
17 (26.6)
160 (28.0)
April–June
126 (24.9)
12 (18.8)
127 (22.2)
July–September
139 (27.5)
15 (23.4)
140 (24.5)
October–December
129 (25.5)
20 (31.3)
145 (25.3)
Overall 506 (100) 64 (100) 572 (100)

aInternational Classification of Diseases, 9th Revision, Clinical Modification.
bSource: Office of Statewide Health Planning and Development, Patient Discharge Data, Public Version A.
cArboviral encephalitis was diagnosed in Sacramento in 1992 (n = 1) and 1997 (n = 1), in Yuba in 1999 (n = 1), in Imperial in 1997 (n = 1), and in Riverside in 1991 (n = 3), 1994 (n = 2), and 1997 (n = 1).
dTotal number of encephalitis diagnoses in Sacramento-Yolo and Imperial-Riverside is greater than the number of encephalitis patients because some patients had two or more encephalitis diagnoses.

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