The Howie Code: what are the real costs?

The costs of implementing the Code of Practice for the Prevention of Infection in Clinical Laboratories appear to have been inflated in various ways. These include: alterations and improvements not required by the Code; rehabilitation of neglected buildings to conform with the requirements of the Health and Safety at Work Act; correction of poor design in recently built laboratories; suboptimal management and courses of instruction; and numerous committees.

Diphtheria: the logistics of mass swabbing

Although diphtheria is a rare disease it is necessary to swab contacts of all cases in order to identify carriers. The selection of individuals who should be swabbed and the organisation of mass swabbing so that there is the minimum of delay between collection, culture and reporting are described. With this organisation it is possible for a laboratory to culture at least 1000 swabs in any one day.

Subdivision of Mycobacterium tuberculosis into five variants for epidemiological purposes: methods and nomenclature

Virulent strains of Mycobacterium tuberculosis isolated from humans are divisible into five variants by using four tests: oxygen requirement (aerobic or microaerophilic), nitrate reductase activity, susceptibility to pyrazinamide (60 micrograms/ml) and susceptibility to thiophene-2-carboxylic acid hydrazide (5 micrograms/ml). The five variants are referred to as Classical human, Asian human, bovine, African I and African II. The relation of these variants to previously described types is discussed. This simple division has been shown to be useful in epidemiological studies.

Low incidence of rifampicin-resistant tubercle bacilli

In a six-year survey 10(0.15%) of 6849 patients with European names and 31 (1.0%) of 3079 patients with non-European names yielded cultures of Mycobacterium tuberculosis that were resistant to rifampicin. Only two of each group had organisms resistant to rifampicin alone. Resistance to one or more other antituberculous drugs was found in eight of the European and 29 of the non-European group. Two patients in each group were known to have received treatment for the first time in the United Kingdom; 17 of the non-Europeans were known to have been treated abroad; precise information was not available for the other 12. The overall six-year incidence of patients with rifampicin-resistant M tuberculosis was only 0.41%. The very low incidence among Europeans is probably the result of stricter regimens than are possible in some other areas.

"Classical" and "Asian" variants of Mycobacterium tuberculosis isolated in South East England 1977-1980

Strains of Mycobacterium tuberculosis were divided into 'classical' and 'Asian' types according to their susceptibility to thiophen-2-carboxylic acid hydrazide (TCH). A study of 6638 new cases of tuberculosis showed that there was a much higher incidence of non-pulmonary disease among Asian than among European patients, and that the TCH-sensitive 'Asian' type of organism was much commoner among the former. There was, however, no correlation between the site of disease and the type of organism. Resistance to antituberculosis drugs was more frequent among strains from Asian patients but there was no correlation between such resistance and susceptibility to TCH. No evidence was therefore found to link differences in the clinical features of tuberculosis in the two populations of patients to the type to organism.

A study of bovine strains of Mycobacterium tuberculosis isolated from humans in South-East England, 1977-1979

Bovine strains of Mycobacterium tuberculosis were isolated from 137 of 5021 cases of tuberculosis (2.7%) occurring in South East England during the years 1977 to 1979. These were divisible into 'classical' and 'Afro-Asian' bovine strains according to their susceptibility to pyrazinamide. Classical strains were the predominant type among the Europeans and Afro-Asian types were commoner in immigrants. Bovine strains caused a high incidence of extrapulmonary disease in both ethnic groups and there was a significant relationship between renal disease and 'classical' strains. The age and sex distributions of bovine strains were similar to those of human strains in both ethnic groups. It was considered that these bovine strains were transmitted from human to human by the pulmonary route.

Sensitivity of opportunist mycobacteria to rifampicin and ethambutol

A total of 1237 strains of opportunist mycobacteria were tested for sensitivity to rifampicin and ethambutol. Most strains of Mycobacterium kansasii and all strains of M. marinum tested were sensitive to both drugs. A variable pattern was given by M. xenopi strains, but a general resistance was observed with the M. avium--intracellulare--scrofulaceum group. All strains of M. fortuitum and M. chelonei were highly resistant. Scotochromogens were mostly sensitive to ethambutol, but there was variable resistance to rifampicin. These properties may be useful in identification of species. No acquired resistance was found in follow-up cultures from confirmed cases of mycobacterioses, but details of therapy, if any, were not known.

Identification of tubercle bacilli

Initial screening of tubercle bacilli with 2-thiophene carboxylic acid hydrazide (TCH) or 2-furoic acid hydrazide (FAH) separates them into two groups. Resistant strains are Mycobacterium tuberculosis. Sensitive strains include M. tuberculosis, M. bovis and BCG which are separated by nitratase and oxygen requirement tests. Pyrazinamide sensitivity tests allow M. bovis and M. africanum to be identified. The niacin test is not used. Most strains of M. tuberculosis from Europeans are resistant to TCH and FAH and are in phage groups A and B, while most strains from Asians are sensitive and are in phage group I.

Hydroxylamine sensitivity and salt tolerance in screening and identifying mycobacteria

Hydroxylamine sensitivity offered no advantage over p-nitrobenzoic acid in distinguishing between tubercle bacilli and other (opportunist and non-significant) mycobacteria. It was of limited use in identification procedures. Salt tolerance assisted in the identification of strains which may be Mycobacterium triviale and M. chelonei var borstelense.