An epidemic of acute haemorrhagic conjunctivitis caused by enterovirus 70 in Okinawa, Japan, in 1994

Background: Although enterovirus 70 (EV70) has been identified as the major aetiological agent of acute haemorrhagic conjunctivities (ACH),no EV70 strain has been isolated by cell culture method since 1988. Therefore, recent clinical and epidemiological characteristics of AHC caused by EV70 have nor been clarified. Methods: Clinical and serological studies were carried out on patients during the AHC epidemic in Okinawa, Japan, in 1994 in which 7509 cases were reported by national epidemiological surveillance. EV70 was confirmed as the causative agent by reverse-transcription polymerase chain reaction. Results: The 11-15 years age group contained the highest number of cases (62% of the total). Conjunctival hyperaemia was present in all patients, and subconjunctival haemorrhage, superficial punctate keratitis and preauricular lymphadenopathy were present in 24.0%, 11.7% and 9.3% of AHC cases, respectively. No neurological complication was observed in this epidemic. Out of 31 paired serum samples, 10 pairs showed a fourfold rise in antibody level to EV70. None of the paired serum samples showed a fourfold rise in antibody level to Coxsackie A24 variant virus. Conclusion: These findings demonstrate that the clinical features of AHC observed in this study were milder than those reported previously, in contrast to the high transmission rate during an epidemic. Changes in clinical features of AHC, such as a low incidence of subconjunctival haemorrhage and disappearance of neurological complications, might be due to biological transformation of EV70, It should be noted that EV70 is still an important aetiological agent of exploxive epidemics of AHC.