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34. Virological investigation of the disease was maintained through- out the year. A poliomyelitis faecal survey among normal children under five was carried out in July-September. The result showed that the excretor rate of 'vaccine' types of poliovirus was about 0,96 per cent among a total of 518 children included in the survey. The 'wild' types of poliovirus (type 3) were detected in two children giving an excretor rate of 0.38 per cent. The findings in the survey indicated the continuing existence of 'wild' poliovirus type 3 in the community--responsible for nearly all clinical cases since 1970,

Influenza

35. The surveillance programme for influenza was continued on a year-round basis. Several general out-patient clinics have been designated as influenza surveillance centres, and these reported regularly the number of influenza-like illnesses seen. The government virus unit continued to function as a World Health Organization National Influenza Centre during the year, and virological investigations of throat swabbings and throat washings were carried out routinely on samples taken from influenza-like cases. Deaths from influenza, pneu- monia and bronchitis were recorded regularly as part of the programmes of epidemiological surveillance of the disease.

36. The disease occurred sporadically from February to September 1971, but high incidences of influenza A and B virus infections were observed in June and July respectively. The most prevalents strain of influenza A virus was A/Hong Kong/68 (H3N2). A/England/878/69 variant was delected twice in March, and a new antigenic variant A/ Hong Kong/107/71 was detected in September. The latter strain was closely studied by both the government virus unit and the World Influenza Centre.

Teranis

37. This disease, although not notifiable, was recorded during the period under review, as in the past, with reasonable accuracy owing to the severity of the symptoms, requiring hospitalization of clinical cases. In past years, approximately half the cases reported were among the new-born whose births had not been attended by trained staff and who had been exposed to various hazards from unsterile equipment. In

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1971, tetanus neonatorum was responsible for only 15.5 per cent of the recorded cases, and infant mortality from such infection fell from 1.2 deaths per 1,000 in 1951 to 0.117 deaths in 1971.

Viral Hepatitis

38. Notification of this disease remained voluntary. A total of 357 cases was notified in 1971. Most cases were among adolescents and adults, and a higher proportion was found among males. During the year, steps were taken to promote better and more complete reporting and investigation of the disease.

Japanese B encephalitis

39. This disease among bumans is encountered occasionally in Hong Kong, and during the year, four cases were reported. All were from the New Territories, and all were children under 10. The disease is trans- mitted by a mosquito vector and the important species known to transmit the disease is Culex tritaeniorhynchus. This mosquito is found in the rural areas of the New Territories.

40. Humans and horses are only incidental hosts to the Japanese encephalitis virus, but pigs are considered important reservoirs. In June, five horses at the Royal Hong Kong Jockey Club stables at Beas River, New Territories, were found to be infected by the virus. Preventive and control measures against the disease were immediately reinforced, including mosquito control and personal anti-mosquito measures. The affected borses were isolated. There was no connection between the occurrence of the four human cases mentioned earlier, which came from other areas of the New Territories, and this outbreak. A serological survey of the incidence of the Japanesc encephalitis virus infection among horses was subsequently carried out. There was no evidence of extensive vírus dissemination among the horses. (See paragraph 91 for details).

Acute Kerato-Conjunctivitis

41. This disease is of worldwide distribution. It occurs as sporadic cases, but epidemics are often reported. In the beginning of August 1971, there was a sudden increase in the number of patients attending the three government ophthalmic clinics for treatment of acute conjunc- tivitis. Between August 5 and 7, a total of 1,571 cases was treated.

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