The 1968 influenza outbreak in Thailand

400 DISCUSSION PAPERS-SESSION I on board. From 7 of these cases influenza virus similar to A2/Hong Kong/68 was isolated. Only 8 cases of typical influenza were reported in the hospitals in the city of Madras on 9 September 1968. The number increased rapidly day by day, reaching 7661 on 17 September. Subsequently it declined to 68 on 31 October. During the period 9 September to 31 October, 84 511 patients were treated in the hospitals in Madras City, which has a population of 2 million. The attack rate was there- fore 4.2%. It is estimated that an equal number of persons were treated by the private practitioners in the city, thus giving an attack rate of 8.4%. Subsequently, the epidemic spread to different areas in Madras State. Cases were reported in Chingleput, Conjeevaram, Pondicherry, Vellore, Coimbatore, and the Nilgiris during the latter part of September. The epidemic spread to Madurai, Tirupur, Karur, Trichy, Tanjore, and Palni during the first half of October. Tirunelveli, Ramnad and Salem were affected during the middle and latter part of October. Influenza activity declined during the second half of November and December in Madras State. The isolation of 2 strains of Hong Kong virus, one at Coonoor on 29 August and the other at Ootacamund, about 350 miles (560 km) from Madras on 31 August indicated that the virus had been seeded even before the arrival of the S.S. Rajila from Singapore on 8 September 1968. The main epidemic spread through the Indian subcontinent within 20 weeks. In each area the pattern was one of sweeping spread through the most crowded cities followed by a relatively slow spread across villages and towns. All age-groups were involved, although the mani- festation of the disease appeared to be more severe among children. Persons who had an attack of Asian influenza in 1957 and those who had an attack of proved A2 influenza subsequently generally escaped infec- tion by the Hong Kong virus. All patients complained of headache, generalized aches and pains, malaise, and fever. Some com- plained of backache, sore throat, and cough. Very few patients had respiratory complications such as pneumonia and bronchopneumonia. Sputum cul- tures from such cases showed nonhaemolytic strepto- cocci and staphylococci. Electrocardiographic stu- dies showed evidence of myocardial inflammation. Gastrointestinal symptoms such as vomiting, jaun- dice, and hiccup were rare compared with the epidemic of 1957. A few patients with clinical signs of encephalitis or myelitis and meningism associated with mild disorientation were also encountered. On the whole the disease was relatively mild with few complications. From Madras City and other towns in the State, 146 strains of influenza virus were isolated from 29 August to 31 December 1968. All of them were similar to A2/Hong Kong/68 virus. Throughout this period, when over 442 throat gargles were processed, not one strain of type B virus was isolated, indicating the absence of influenza virus B infection. The 1968 Influenza Outbreak in Thailand by CHANINTHORN SUVONGSE a About 1 month after the outbreak of influenza in Hong Kong on 13 July 1968,b febrile illness was reported among US troops at the US Air Force Base, Korat Province, in the north-eastern part of Thailand. Within 3 weeks the number of cases reached epidemic level. The US component of the SEATO Medical Research Laboratory and the a SEATO Medical Research Laboratory, Bangkok, Thai- land. b Thong-Charoen, P. et al. (1969) J. med. Ass. Thailand, 52, No. 9. Faculty of Public Health, Mahidol University, made a detailed study among US troops in that area. Following the outbreak, the disease seemed to spread rapidly to Bangkok and various other provinces. The epidemic began in August, reached its peak in October, and declined during the last part of Novem- ber. In general, clinical symptoms were mild and the incidence of complications was relatively low. No deaths definitely attributable to influenza were reported. In Bangkok health authorities were alerted to- 2381c 1968 INFLUENZA OUTBREAK IN THAILAND TABLE I AGE AND SEX DISTRIBUTIONS OF PATIENTS WITH CLINICAL SYMPTOMS OF INFLUENZA-LIKE ILLNESS, BANGKOK, AUGUST 1968 Siriraj Hospital Vachira Hospital Private practitioners Age (years) No. of No. of Pretae No. of No. of Pretgl No. of No. of Pretg _ _ _ males females _ _ males females Percentage males females Percent <5 51 41 24 20 127 92 6-10 37 27 23 24 187 146 46 42 59 11-15 48 30 38 30 262 258 16-20 77 41 92 65 163 256 21-30 72 73 120 89 117 187 31-40 59 55 62 39 131 188 41-50 28 32 54 31 33 58 127 117 41 51-60 23 32 16 23 75 59 _61 12 20 19 11 18 38 Total 407 351 100 425 334 100 1 207 1 341 100 wards the end of August, when 6 medical students developed an influenza-like illness b and increasing numbers of patients with similar symptoms were seen in out-patient departments of various hospitals. Epidemiological data were obtained from 2 large hospitals in Bangkok (Siriraj and Vachira hospitals). Questionnaires were also sent to various private practitioners asking about influenza-like signs and symptoms in their patients. The age and sex distri- butions of patients are shown in Table 1. The data indicate that all age-groups were affected and that the male-to-female ratio was almost 1 :1. The viral agents isolated appeared to be homo- geneous and were shown by the HI test to be similar to the influenza A2/Hong Kong/68 strain (see Tables 2 and 3). For serological investigation, 104 pairs of sera were collected 1 week apart. A 4-fold or greater TABLE 2 HI TITRES OF VIRUSES ISOLATED AT SIRIRAJ HOSPITAL, BANGKOK, DURING THE 1968 INFLUENZA EPIDEMIC Titre to the following hyperimmune rooster antisera Virus isolated A2/Bangkok/18/68 A2/Hong Kong/1/68 A2/Aichi/2/68 A2/Bangkok/18/68 640 1 280 320 A2/Bangkok/21/68 320 1 280 320 A2/Bangkok/24/68 640 2 560 640 A2/Bangkok/37/68 640 640 640 A2/Aichi/2/68 640 1 280 640 A2/Singapore/1/57 >20 - >20 401 402 DISCUSSION PAPERS-SESSION I TABLE 3 Hi TITRES OF VIRUSES ISOLATED AT THE NATIONAL INFLUENZA CENTRE, BANGKOK, 1968 Titre to the following hyperimmune ferret antisera irusisolated-A2/Singapore/ A2/England/ A2/Tokyo/ A2/Hong Kong/ 1/57 12/64 3/67 1/68 A2/Singapore/1/57 >2 560 240 80 160 A2/England/12/64 480 >2 560 64 80 A2/Tokyo/3/67 <20 30 160 <20 A2/Hong Kong/1/68 80 <20 <20 1 920 A2/Bangkok/2/68 60 <20 <20 1 920 rise in HI antibody titre was demonstrated in 52 cases. Based on inquiries made to 6630 families (1.7% of the total population) in Bangkok, the attack rate was estimated to be 47 per thousand and the total number of patients in this city was approximately 150000. However, since the influenza during this outbreak was mild and since analysis was based on clinical diagnosis only, the extent of the outbreak may have been underestimated. Epidemiological Data on Hong Kong Influenza in France by R. SOHIER a & M. HENRY b Hong Kong influenza was first observed in France in the last 2 weeks of January 1969, when sporadic cases occurred in the district of Paris, and developed progressively throughout the country. The peak was reached in March, the incidence began to decrease in April, and the last cases were observed in May. The incidence remained relatively low and the ex- tent moderate, and the disease was mild or of moder- ate severity. In many parts of the country, only spo- radic cases were observed. Some local outbreaks were reported in towns or villages. Generally, influ- enza (confirmed by virus isolation or by serological tests) was observed in all age-groups, but in some outbreaks the greatest incidence occurred in children aged 4 years or less; in other outbreaks it occurred among those aged 15-24 years. The disease occurred less frequently among the older age-groups. a Virology Department, National Public Health Labora- tory, Lyon, France. b Faculty of Medicine. University of Lyon, France. It was difficult to obtain comprehensive mortality data, since notification of influenza is not compulsory in France, but deaths from clinically diagnosed cases were reported by some practitioners. Data on such reported cases are collected every year in roughly the same manner, and the figures for the first 4 months of 1967, 1968, and 1969 can be compared. During thlIse past years, all but one of the influenza A2 outbreaks occurred in a period extending from January to April, with a peak in February-March, as we have been able to show by means of a conti- nuous survey performed by CF tests using soluble (nucleocapsidic) type-specific antigen. As shown in the accompanying figure, the number of deaths from influenza during the first 4 months of 1969 was 3186, less than the number for the comparable periods of 1968 and 1967 (7267 and 3472, respectively). The first positive CF test appeared in the course of our continuous surveillance some weeks before the 2381D