Reported cases of hepatitis have been classified into hepatitis A, hepatitis B, non-A non-B hepatitis and unclassified (data on hepatitis markers inconclusive) forms since 1988. The criteria of the classification are listed in table 1. This reporting system has documented the incidence of clinical viral hepatitis. The majority were acute hepatitis while a proportion might be acute-on-chronic diseases.

Classification	Criteria
Hepatitis A	IgM anti-HAV positive
Hepatitis B	IgM anti-HBc positive
NANB	negative for either of the above two
Unclassified	data on hepatitis markers inconclusive

table 1 - classification criteria for the notification of viral hepatitis

The reported incidence of viral hepatitis against time is shown in figure 1 and table 2. It shows that the incidence of hepatitis A essentially dominates that of hepatitis as a whole, accounting for over half of all reported cases each year.

The overall incidence of viral hepatitis was low from 1966 to 1970. A trough occurred in 1970 with a total incidence of only 117. It then gradually increased to 1554 in the year 1980 with two epidemics, in 1972 (729 cases ) and 1975 (1761 cases). A plateau was reached that lasted from 1981 to 1984. A general declining trend was then noted from 1984 to 1995, punctuated by two outbreaks in 1988 (2398 cases) and in 1992 (4357 cases).

year	A	B	NANB	Unclassified	total
66	voluntary reporting since 1966				386
67					218
68					191
69					188
70					117
71					357
72					729
73					509
74	notifiable since 1974				639
75					1761
76					969
77					1008
78					1230
79					964
80					1554
81					1738
82					1814
83					1783
84					1780
85					1601
86					1425
87					1554
88	1187	250	465	496	2398
89	618	136	154	324	1232
90	1362	178	183	261	1984
91	1297	150	200	154	1801
92	3626	157	301	273	4375
93	874	116	203	80	1273
94	557	112	125	41	835
95	489	99	51	27	666
96	253	153	44	18	479

table 2 - reported viral hepatitis from 1966 to 1995

In the 1992 outbreak of hepatitis A. 3626 cases were reported. A breakdown of age and sex is summarized in figure 2. Clinical cases of hepatitis A occurred predominantly in the age group 20-29 (n=1842, 50.8%). The next age group with high incidence was 10-19 (n=770, 21.2%). Hepatitis A was uncommon in age over 50 (n=15, 0.4%).

age group	female	male	total
0-9	160	203	363
10-19	262	508	770
20-29	627	1215	1842
30-39	161	375	536
40-49	35	65	100
50-59	4	8	12
60-69	0	1	1
70-79	0	1	1
80-99	1	0	1
total	1250	2376	3626