Add this into your squid.conf:

# icap squidclamav
icap_enable on
icap_send_client_ip on
icap_send_client_username on
icap_client_username_encode off
icap_client_username_header X-Authenticated-User
icap_preview_enable on
icap_preview_size 1024
icap_service service_avi_req reqmod_precache icap://localhost:1344/squidclamav bypass=off
adaptation_access service_avi_req allow all
icap_service service_avi_resp respmod_precache icap://localhost:1344/squidclamav bypass=on
adaptation_access service_avi_resp allow all