Changes and changing concepts in the biology of group A streptococci and in the epidemiology of streptococcal infections

Concepts of the cellular structure of group A streptococci have been modified by the recognition of surface fimbriae and by problems with the older view of a layered arrangement of cell wall components. Evidence of genetic drift of serologic types and of some increase in the prevalence of erythromycin-resistant strains has appeared. A curiois bimodal age distribution for streptococcal pharyngitis and an increase in the prevalence of non-group A strains has been detected. Despite repeated challenges, the value of throat cultures for confirming the possibility of streptococcal pharyngitis remains firmly established; throat cultures are superior to saliva cultures, which more frequently detect non-group A streptococci. Difficulties in detecting subclinical steptococcal infections and in defining streptococcal infection in children in endemic situations (particularly in separating true streptococcal infection from carriage of streptococci in individuals whose illness is due to some other agent) continue to present problems to clinicians and epidemiologists. The value of school culture surveys and of treatment of asymptomatic family contacts of cases remains uncertain. A 20% bacteriologic failure rate has been reported after intramuscular treatment with benzathine penicillin, but no in vitro evidence of resistance to penicillin has appeared. No adequate explanations are available for the decline in the problem of rheumatic fever in industrialized countries, for its increased recognition in tropical countries, for the failure of rheumatic fever to occur after streptococcal pyoderma, or for the emergence of group B Streptococcus as a predominant bacterial pathogen in newborn infants.

Poststreptococcal acute glomerulonephritis: fact and controversy

Poststreptococcal acute glomerulonephritis is prototypic of the immunologic glomerulonephritides. It most commonly follows streptococcal infection of the pharynx or skin. The diagnosis is usually not difficult when a nephritic clinical presentation (with such manifestations as hematuria, edema, and hypertension) is associated with serologic evidence of recent streptococcal infection and a depressed serum complement concentration. Currently, however, the nephritogenic antigen(s) has not been identified and has not been shown to be the same antigen for all nephritogenic streptococci; it may not even be a part of the infecting organism. The development of a vaccine to prevent this illness from occurring is therefore still not possible. Whether poststreptococcal acute glomerulonephritis progresses to chronic renal failure is still uncertain. Painstaking laboratory research together with careful, prospective long-term follow-up studies of patients with poststreptococcal acute glomerulonephritis may provide some of the answers to these critical questions.

The risk of streptococcal infections in rheumatic and non-rheumatic families: an application of Greenwood's chain-binomial model

Infectious transmission of streptococci in families has been demonstrated to follow Greenwood's chain-binomial model in its simplest form which did not need beta transformation to correct for differences in susceptibility between families. Following the application of this model, an estimate of the risk of acquisition of M-typable group A beta-hemolytic streptococci is given (p = 0.05--0.06). The risk is the same among siblings of rheumatic fever patients and children from non-rheumatic families. This emphasizes that the familial aggregation associated with rheumatic fever is not due to increased susceptibility of such families to streptococcal infections.

Adherence of group A streptococci to pharyngeal cells: a role in the pathogenesis of rheumatic fever

We used an assay in vitro to investigate the possible role of streptococcal adherence to human pharyngeal cells in the pathogenesis of acute rheumatic fever. There was no difference in adherence of rheumatic fever-associated and non-associated strains of group A streptococci to pooled pharyngeal cells of normal people. Likewise, streptococci not associated with rheumatic fever adhered equally well to cells taken from normal people and from patients with rheumatic heart disease. However, the pharyngeal cells of all nine rheumatic heart disease patients tested had increased avidity for adherence for a rheumatic fever-associated strain of streptococcus compared to the pharyngeal cells obtained from age- and sex-matched controls. Increased streptococcal adherence to pharyngeal cells of rheumatic fever-prone patients may play a role in the pathogenesis of rheumatic fever.

Incidence and prognosis of rheumatic carditis in a Belgian hospital. A 10-yr review (1965-1974)

106 cases of first attack of acute rheumatic fever were recorded during a decade (ending in 1974) in a Brussels pediatric clinic. 56 patients were Belgian and 50 were children of immigrants. The incidence of acute carditis was 23% among the former, 46% among the latter (P less than or equal to 0.01), and 34% among the whole group. The frequency of residual heart disease after a 3-yr antistreptococcal prophylaxis fell to 20% among the whole group. The difference in morbidity observed between Belgian children and children of immigrants calls for a prospective epidemiological study.

Tropical acute rheumatic fever and associated streptococcal infections compared with concurrent acute glomerulonephritis

Ninety-three patients with acute rheumatic fever and 195 patients with acute glomerulonephritis were observed in Trinidad during an outbreak of scabies with a high incidence of secondary streptococcal infections. Clinical and laboratory manifestations of ARF were the same as those seen in temperate zones, except that antistreptolysin O titers were less markedly increased. The patients with ARF were similar to those with AGN in respect to sex, race, location of residence, and living conditions, but were older and had markedly fewer skin infections. Currently prevalent nephritogenic streptococcal strains never were isolated from patients with ARF even when M55 streptococci appeared and led to an epidemic of AGN.

Genetic damage from diagnostic radiation

Using the data from the Tri-State Leukemia Survey and a mathematical model, the hypothesis that low levels of diagnostic radiation produce severe genetic damage that is expressed in the child of the exposed person as leukemia and other diseases is tested. It is estimated that for about 1% of the exposed persons who are affected by radiation, there is a 50-fold increase in the risk of leukemia and a five-fold increase in certain other diseases.

The changing picture of rheumatic fever

Rheumatic fever has decreased in frequency and severity, but the disease has not been eradicated in this country, especially in low socioeconomic populations. Carditis is less common, and changes in the frequency of other rheumatic manifestations such as chorea has made the clinical diagnosis more difficult. Streptococcal antibody tests are still the most useful laboratory aid, but care must be taken against overinterpretation. The search for the answer to the pathogenesis puzzle continues. Until the nature of the disease is better understood, it is unlikely that rheumatic fever will be eradicated. In the meantime, however, the incidence of the disease can be reduced further by improved medical care for deprived populations.