SOME group-A streptococci cause the appearance of opacity in horse serum (Ward and Rudd, 1938). The production of the opacity factor (OF) is confined to members of certain serotypes (Keogh and Simmons, 1940;Gooder, 1961), and the OF of each serotype is antigenically specific (Top and Wannamaker, 1968a). Widdowson, Maxted and Grant (1970) confirmed the serological specificity of the OF and showed that it corresponded exactly to that of the M type of the streptococcus that produces it. The examination of a limited number of strains of each M type (Widdowson et al., 1970; and our unpublished observations) suggested that OF is produced by all members of 16 welldefined M types, and by a number of other types not so far established by international agreement.We have now made a more sytematic examination of the distribution of OF among strains of group-A streptococci sent to us for typing, and have investigated the use of the serum opacity reaction (SOR), and of its neutralisation by specific antisera, in routine typing and as a means of indentifying hitherto unrecognised streptococcal serotypes. MATERIALS AND METHODSStreptococci Strains used to produce antisera to OF in rabbits were the standard type strains used in the Streptococcus Reference Laboratory for the production of M antisera. Other strains sent to us for type identification from numerous laboratories were used in studies of the distribution of OF.Cultural methods Oxoid Todd-Hewitt Broth with the addition of 1 per cent. Neopeptone was seeded with a loopful of growth from solid medium and incubated overnight at 37°C. These cultures were used for the detection both of OF and of M antigen. Typing techniqueThe methods used in the Streptococcus Reference Laboratory for the preparation of typing sera and for M and T typing are those described by Williams (1958). M antigen was ~

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The water quality objective or indicator of bathing beaches is established on the basis of epidemiological data of swimming-related illnesses in the local population. It needs to be updated and refined in light of changes in the composition, health status and recreational activities of the community. A major epidemiological study was conducted in Hong Kong in 1992 involving interviewing 25000 beach-goers on the health effects of exposure to bathing water. The results indicated that the total incidence of swimming-related illness symptoms was 41 per 1000, higher than the 30 per 1000 found in 1987. Eye, skin and respiratory symptoms were 2-20 times more prevalent in swimmers than in non-swimmers. Only gastrointestinal (GI) symptoms were directly related to the pollution level and bacterial content of beach water. Turbidity of beach water was closely linked with GI and highly credible GI symptoms and might be used as a monitoring tool and a parameter in the beach water quality objective. There was also a direct correlation between GI symptoms and the number of Clostridium perfringens, Aeromonas spp., Vibrio cholerae (non-O1) in beach water. No direct relationship between GI symptoms and E. coli or faecal coliforms could be identified in this study.

The recent epidemic of acute glomerulonephritis in Trinidad had two peaks, separated by an interval of about 6 months.Evidence is presented that there were in fact two successive but overlapping epidemics, the first due to streptococci of provisional M-type 55, and the second to streptococci of M-type 49.

The group G streptococcus has generally not been considered a prominent pathogen. In a 1982 study of the colonization rate by beta-haemolytic streptococci in apparently healthy children, age 5-11 years, 25 of 69 isolates belonged to group G. This surprisingly high rate of group G colonization (14.3%) led to a retrospective study of school surveys in 1967 which showed that the colonization rate with this organism was 2.3% (range 1.3-3.5%). A review of bacitracin-sensitive streptococcal isolates from hospital admissions of patients with acute glomerulonephritis (AGN), rheumatic fever, and their siblings, between January 1967 and July 1980, was conducted. Of 1063 bacitracin-sensitive isolates, 63 were group G, and 52 of these were isolated from AGN patients and their siblings, i.e. 7 from skin lesions of AGN patients, 40 from the throats of siblings and only 5 from the skins of the siblings. The other 11 group G isolates were from rheumatic-fever patients and their siblings. Thus, the group G colonization rate fluctuates in the population. The isolation of only group G streptococci from skin lesions of patients with AGN suggests a possible association between group G streptococcal pyoderma and acute post-streptococcal glomerulonephritis.