Delayed-type hypersensitivity, mycobacterial vaccines and protective immunity

There is a longstanding debate over the implications of natural and vaccine-induced delayed type hypertensivity for protective immunity to mycobacterial infections. The identification of correlates of vaccine-induced protective immunity should help explain the inconsistent behaviour of BCG vaccines in different populations and assist in efforts to devise improved vaccines. More than 70,000 subjects in Karonga District, northern Malawi were skin tested with soluble antigens of the tubercle and leprosy bacilli, and then followed up for five years for tuberculosis and leprosy incidence. Incidence rate ratios were calculated to compare subjects with different levels of prior skin test sensitivity, after controlling for the effects of age, sex and previous BCG vaccination. BCG vaccination protected against leprosy without persistent delayed-type hypersensitivity to tuberculin or to soluble antigens of the leprosy bacillus. In subjects who had not received BCG, hypersensitivity to tuberculin or to antigens of the leprosy bacillus was associated with strong protection against leprosy. In BCG-vaccinated and unvaccinated subjects, there was a J-shaped relation between hypersensitivity to tuberculin and subsequent rates of tuberculosis, with lowest rates associated with low grade sensitivity (induration 1-10 mm). This study shows that delayed-type hypersensitivity to mycobacterial antigens has different implications for tuberculosis and leprosy: low-level hypersensitivity (probably attributable to environmental mycobacteria) is associated with protection, but persistent vaccine-associated hypersensitivity to mycobacterial antigens is not a correlate of vaccine-derived protection against mycobacterial diseases.

Treatment of superficial mycoses in the tropics: Whitfield's ointment versus clotrimazole

BACKGROUND

In tropical primary health care, essential drugs should be safe, effective, and as inexpensive as possible. To treat the very common dermatophyte infections of the skin, one may use inexpensive Whitfield's preparations, more expensive topical imidazole derivatives, or extremely expensive oral antifungals. Because a cream base is felt to be more appropriate than an ointment in tropical conditions, we wanted to compare the effectiveness of Whitfield's cream and a topical imidazole derivative in field conditions in the tropics.

METHODS

A double-blind trial was performed involving 153 patients with a dermatophyte infection of the skin in Karonga District, Northern Malawi, including 25 patients who were HIV-1-seropositive, comparing Whitfield's cream with clotrimazole cream.

RESULTS

75 patients were treated with Whitfield's cream and 78 with clotrimazole cream for a period of 6 weeks. Cure rates ranged from 80% to over 90% depending on the definition of cure. If positive cultures after treatment were used as criterion for treatment failure, six were found in each treatment group. One in each treatment failure group was an HIV-1-seropositive patient.

CONCLUSIONS

The great majority of patients in the tropics with a dermatophyte infection of the skin can be cured with a topical antimycotic preparation and do not need expensive oral therapy. This also proved to be valid for HIV-1-seropositive patients. Whitfield's cream and clotrimazole cream are both very effective. The lower cost makes Whitfield's cream the treatment of choice in dermatophyte infections of the skin in tropical primary health care.

Extended schooling and good housing conditions are associated with reduced risk of leprosy in rural Malawi

Incidence rates of leprosy in Karonga District, northern Malawi, are analyzed by duration of schooling and housing conditions, controlling for age, sex, BCG scar and geographical zone of the household. There is a strong inverse relationship between the number of completed years of schooling and leprosy risk. Good housing conditions are also associated with a decreased risk of developing leprosy in this population. The effect of housing is seen most strongly in young people. It is hypothesized that schooling changes behavior and housing determines environment in ways which are relevant for the transmission of Mycobacterium leprae or for the appropriate priming of the immune system.

Incidence rates of leprosy in Karonga District, northern Malawi: patterns by age, sex, BCG status and classification

This paper describes incidence rates by age, sex, prior BCG status and classification in Karonga District, northern Malawi. New cases (489) were identified among 83,500 individuals followed for an average of 5 years (1.12 cases per 1000 person years). Only 29 (6%) of the incident cases were multibacillary. Incidence rates generally were higher among females than males, and increased steadily with age. Although the highest incidence rates of disease were recorded among young adults without BCG scars (males 15-19; females 20-24), these peaks were less dramatic than those reported among young adults in The Philippines and Norway. In the absence of historical data and data on infection status, it is not possible to assess to what extent these peaks may reflect either greater exposure or greater susceptibility to disease among adolescents or young adults. The incidence rates of leprosy among individuals with a prior recorded BCG scar were approximately half those of individuals lacking a scar, at all ages. Since BCG had been introduced into this population only during the 1970s, this provides strong evidence for the effectiveness of BCG when given to adults. It was estimated that past vaccination of approximately 40% of the district population had reduced the overall incidence rate of leprosy by 18%, and that this impact would increase with aging of the vaccinated cohorts. A retrospective examination of the detailed records of initial examinations revealed that 62 (13%) of the incidence cases were recorded as having skin hypopigmentation or blemishes, at the site of subsequent confirmed leprosy lesions, several months or years before they were suspected of having leprosy. The nonspecificity of these lesions, some of which were probably attributable to Mycobacterium leprae infection, highlights the difficulty of diagnosing leprosy in its earliest forms.

The Karonga Prevention Trial: a leprosy and tuberculosis vaccine trial in northern Malaŵi. I. Methods of the vaccination phase

In this report the methods of the Karonga Prevention Trial, a double-blind leprosy and tuberculosis vaccine trial in Karonga District, Northern Malaŵi, are described in detail. During a total population house-to-house survey, which lasted from November 1985 until August 1989, 121,008 people (57,892 males and 63,116 females) were vaccinated. A further 5835 people refused vaccination and 5757 were ineligible for vaccination, 2652 of them because they had a history or signs of leprosy, or because they were suspected to have early leprosy. A total of 66,145 individuals, without evidence of prior BCG vaccination, received one of the following: BCG, BCG + 5 x 10(7) killed Mycobacterium leprae, or BCG + 6 x 10(8) killed M. leprae; 54,863 individuals found with a typical or a doubtful BCG scar received either placebo or BCG, or (from mid-1987 onwards) BCG + 6 x 10(8) killed M. leprae. Side-effects were not looked for systematically, but 4 individuals self-reported with glandular abscesses, 9 with large post-vaccination ulcers (> 25 mm in diameter) and 2 with ulcers which persisted for more than 1 year. BCG vials collected from paraffin refrigerators in the field showed satisfactory concentrations of viable BCG throughout the trial. Post-vaccination skin test (RT23 and M. leprae soluble antigen) results and post-vaccination ulcer rates indicate that few mistakes were made in the field when recording the vaccine codes.

Elevated opsonic activity for Porphyromonas (Bacteroides) gingivalis in serum from patients with a history of destructive periodontal disease. A case: control study

We have measured the opsonic capacity of serum for the phagocytosis of Porphyromonas (Bacteroides) gingivalis by polymorphonuclear leucocytes (PMN) in 35 patients with a history of destructive periodontitis and 35 matched control subjects. The serum from cases, tested at concentrations of 8% and 0.8% opsonised P. gingivalis for phagocytosis by PMN to a level significantly greater than controls (p < 0.0001 and < 0.01 respectively). IgG antibody levels to P. gingivalis whole cells estimated by ELISA were also significantly higher in the cases (p < 0.0001). The IgG antibody levels correlated significantly with the opsonic capacity of the serum tested at 8% concentration in controls (r = 0.371, p = 0.03) but not in cases (r = 0.235, p = 0.17); in 0.8% serum, the opsonic capacity of the cases and controls were not significantly correlated. Elevated opsonisation by serum was a significant predictor that a subject was a case rather than a control, even after allowing for the effect of elevated IgG antibody in the cases. The data suggest that an elevated capacity of serum to opsonise P. gingivalis is a distinctive feature in patients with past destructive periodontal disease.

Extent, origin, and implications of observer variation in the histopathological diagnosis of suspected leprosy

Identical slides from 100 biopsies obtained from individuals suspected of having leprosy, ascertained in a total population survey in Malawi, were examined twice, independently, by three histopathologists. Results were reported in a standard protocol, and were compared among themselves and with a standardized clinical assessment of each "suspect." The proportion of biopsies considered to show definite evidence of leprosy ranged from 29 to 55 among the six evaluations (twice by each of three histopathologists). Comparisons of variations within and between histopathologists revealed three different patterns. Two of the pathologists were very consistent as individuals, but differed markedly between themselves in that one was the least inclined and the other the most inclined to report definite evidence of leprosy. The third pathologist was less consistent, reporting appreciably more definite leprosy on the first than on the second examination of the same biopsies. Although acid-fast bacilli (AFB) were reported on at least 1 examination in 40 of the biopsies, they were observed in all six examinations of only six of the biopsies. There was greater agreement regarding classification than regarding diagnosis, except with reference to the indeterminate category which was employed more frequently by one histopathologist than by the other two. A workshop of participants at the end of the investigation highlighted several reasons for the variations observed. The fact that AFB were reported in only nine biopsies by one histopathologist but in 33 by another reveals the importance of the examination method and time in arriving at a diagnosis of leprosy. The differences in the interpretation of cellular evidence of inflammation revealed the need for further studies of nerve-related pathology in nonleprosy conditions to serve as a reference against which to judge possible evidence of leprosy per se.

Human immunodeficiency virus: GACPAT and GACELISA as diagnostic tests for antibodies in urine

Testing for antibodies to human immunodeficiency virus (HIV) in urine may be of use in epidemiological studies. We collected 336 paired urine and serum samples from subjects in Karonga District, northern Malawi: 86 (25.6%) of the serum samples were HIV positive. Serum results were compared with those from immunoglobulin (Ig) G antibody-capture particle adherence tests (GACPAT) and IgG antibody-capture enzyme-linked immunosorbent assay (GACELISA) on the corresponding urine samples performed independently in 2 laboratories. The minimum observed relative sensitivity and specificity of GACPAT were 96.5% and 98.8% respectively; the specificity could be raised by using a protocol involving re-testing of reactive samples to determine end-point titre. For GACELISA, the observed relative sensitivity and specificity were 98.8% and 99.2% respectively. Such assays may be useful either as a primary screen in populations where urine samples are considerably easier to obtain than serum samples, or as an alternative test for individuals unwilling to provide a serum sample.

Long-term active surveillance of leprosy suspects--what are the likely returns?

Data are presented from the Karonga District in Northern Malaŵi on the long-term follow up of 277 leprosy suspects who were not given antileprosy treatment or kept on active surveillance. Individuals who were started on antileprosy treatment within a year after leprosy was first suspected, usually on the basis of histopathology results, are excluded from this analysis, because their active surveillance would not usually cause an organizational or financial problem for leprosy control projects. After an average follow-up period of 4.5 years 35 of the 277 suspects included in the analysis (13%) were diagnosed with what we consider to be 'unequivocal' leprosy, and 3 of the 35 had developed disabilities. In 211/277 (76%) all signs of leprosy had disappeared completely. Comparing clinical certainties at first and last examinations and comparing clinical with histopathological certainties at last examinations it is estimated that up to 50% of the 35 cases of unequivocal leprosy which 'arose' in this group were attributable to misdiagnosis at the 1st or 2nd examination rather than to genuine progression of the disease. This estimate is compatible with an overall sensitivity of 90% and an overall specificity of 95% at each examination. Leprosy suspects with 1 cardinal sign of leprosy, either a typical lesion without loss of sensation, or loss of sensation in an otherwise untypical lesion, should be considered a high-risk group in that approximately 25% of such suspects (19/78) were later found with unequivocal leprosy. Policies towards such suspects should be formulated by leprosy control projects.

Associations between volume and flow rate of gingival crevicular fluid and clinical assessments of gingival inflammation in a population of British male adolescents

Gingival crevicular fluid (GCF) sampling was performed on 2 occasions separated by 1 year, at 2 sites in the mouths of 102 male adolescents, mean age 17.85 years. Samples were collected onto 5 filter paper strips which were sequentially applied to the mouth of the crevice over a 9-min collection period. Volume and flow rates of GCF were determined for each site and were compared with clinical measurements of plaque, gingival colour, bleeding, gingival index (GI) and pocket depth, using a general linear models (GLM) procedure. While the initial volume of GCF showed no association with any clinical measurement, there was an association between flow rate of GCF and gingival colour. The volume of GCF collected in the final, 5th sample was associated with the GI. The sample site strongly influenced all measures of GCF volume. It is proposed that the flow rate of GCF may be a better indicator of gingival inflammation than the more imprecise clinical assessments of inflammation, since GCF flow rates more precisely reflect changes in tissue permeability. The association between the final sample, collected after 9 min, and clinical measurements, was probably a reflection of the association between clinically-detectable inflammation and the susceptibility of the site to mild irritation.

Elevated levels of the IgG2 subclass in serum from patients with a history of destructive periodontal disease. A case-control study

The levels of the 4 subclasses of IgG were estimated in the serum from 35 patients with a history of chronic periodontitis and 35 matched controls. The levels of IgG2 were significantly (P less than 0.019) elevated in the patients (3.756 g l-1) compared to the controls (2.882 g l-1). The data suggest that the predominant antibody response to periodontal pathogens in periodontitis may be directed against carbohydrate or glycolipid antigens.

Efficacy of BCG vaccine against leprosy and tuberculosis in northern Malawi

Protection afforded by BCG (bacillus Calmette-Guérin) vaccines against tuberculosis and leprosy varies widely between different populations. In the only controlled trial which assessed protective efficacy of BCG (Danish and Pasteur strains) against both diseases, there was slightly more protection against leprosy than against tuberculosis. We have studied the protective efficacy of BCG (Glaxo, freeze dried) vaccine against these two diseases in Karonga District, northern Malawi. BCG vaccination was introduced into this population in 1974. Prior information about BCG scar status was available for 83,455 individuals followed up between 1979 and 1989. 414 new cases of leprosy and 180 new cases of tuberculosis were found in this population over that period. Protection was estimated at 50% or greater against leprosy, and there was no evidence for lower protection against multibacillary (84%; 95% confidence interval 26% to 97%) than against paucibacillary (51%; 30% to 66%) disease. There was no statistically significant protection by BCG against tuberculosis in this population. These findings add to the evidence that BCG vaccines afford greater protection against leprosy than against tuberculosis.

Is HIV infection a risk factor for leprosy?

A case control study was undertaken during 1988 and 1989 within the framework of the LEPRA Evaluation Project (LEP)/Karonga Prevention Trail (KPT) in Karonga District, northern Malawi, to investigate whether HIV infection is a risk factor for clinical leprosy. Cases were newly ascertained, biopsy-confirmed, incident leprosy patients older than 14 years of age. Controls were selected from the computer data base on over 170,000 people who form the basis of LEP/KPT. They were matched for sex, age, and area of residence. HIV seropositivity rates were 1.8% (2/112) for incident leprosy cases and 2.4% (24/1011) for controls. The Mantel Haenszel odds ratio is 0.6 (95% confidence interval 0.1-3.3). Thus, no evidence for an association between HIV infection and leprosy incidence has been observed in this population. In a parallel investigation, an odds ratio of 7.4% (95% confidence interval 3.3-16.7) was found for 102 microscopy- and/or culture-confirmed, incident pulmonary tuberculosis cases in the same population during 1989, a result similar to those obtained elsewhere in Africa. Among leprosy relapses, 16.7% (2/12) were HIV positive.

Specific antibody responses to subgingival plaque bacteria as aids to the diagnosis and prognosis of destructive periodontitis

We have reviewed the recent literature on the humoral immune responses to a variety of subgingival plaque bacterial species in patients with destructive periodontal diseases. We do not feel that the information presently available on the specific antibody responses to proposed pathogens such as Bacteroides gingivalis and Actinobacillus actinomycetemcomitans allows antibody responses to be diagnostic. All control subjects without periodontal destruction have antibodies to candidate pathogens but the generally higher levels in patients are not sufficiently elevated to be diagnostic. Nor can they be used to predict the initiation of disease or the onset of new episodes of destruction where disease had previously occurred. Successful treatment of patients may lead to lower levels of antibodies to some organisms, including possible pathogens, and thus support a given species in the aetiopathogenesis of disease. It appears that unsuccessful treatment may be accompanied by continuing high antibody levels to some organisms and further studies may enable this observation to be used to monitor therapy. There is some evidence from serological studies that each destructive episode may be induced by a different bacterial species or consortium. The start of studies using single antigens and the techniques of molecular biology will provide not only antibody-based diagnostic methods but also allow us to determine which bacterial antigens are virulence factors and thus the role of the antibody responses, whether protective or damaging, in the periodontal diseases.

The role of histopathology in the diagnosis and prognosis of periodontal diseases

The histological evaluation of surgical biopsies from affected tissues is a standard way of assessing pathological change and determining treatment in many diseases. In most forms of periodontal disease, however, this approach finds limited application. Here, we review what uses the histopathological approach has in the study and evaluation of the periodontal diseases. Current understanding of the changes in epithelial anatomy during pocket formation, the cellular composition and dynamics of the inflammatory infiltrate and the mechanisms of bone resorption and repair are reviewed from the perspective of the information available from microscopical investigation, including the uses and potential application of modern immunocytochemical methods to these questions. The usefulness of histological study of biopsy material is reassessed in the light of advances made in immunohistochemical techniques and their application to gingival inflammatory infiltrates and epithelia. Such techniques offer immediately valuable research opportunities with potential for diagnostic applications, noteably the recognition of phases of destructive activity and their differentiation from periods of effective host defence.

Statistical models for data from periodontal research

Many factors have been hypothesised either to characterise groups and individuals at risk for periodontal disease or to be markers of periodontal breakdown. In order to identify these as associated either with disease status or progression, a statistical association between the factor and a measure of disease will have to be demonstrated. The statistical modelling of data arising from periodontal research presents special problems. These include the large number of measurements made in each subject, the large magnitude of measurement error compared to the changes in attachment level, the analysis of longitudinal studies, the lack of a measure of instantaneous rate of attachment loss and controversies over the nature of the progression of the disease. We consider statistical methods currently available in the light of these difficulties and identify areas in which further research is necessary.

Detection of high-risk groups and individuals for periodontal diseases: laboratory markers based on the microbiological analysis of subgingival plaque

Periodontal microbiology is reviewed with regard to the potential of certain characteristics to serve as markers of high risk groups or individuals for periodontal diseases. The generally accepted associations between particular organisms and the various periodontal diseases are discussed. The usefulness of various clinical study designs is reviewed. The ecology of the subgingival plaque microflora is discussed and a number of suggestions for future research are made. We have concluded that there is no monospecific aetiology to any of the various periodontal conditions. Nevertheless, we give particular attention to the role of the black-pigmented bacteroides based upon our belief that they, and Bacteroides gingivalis in particular, are fundamental to our understanding of the biology of periodontal diseases in humans and other animals. Consequently, the contribution of its various virulence factors and their potential as markers of disease susceptibility and activity is addressed.

The protein composition of gingival crevicular fluid sampled from male adolescents with no destructive periodontitis: baseline data of a longitudinal study

Gingival crevicular fluid (GCF) is a promising source for markers of destructive periodontal diseases activity. As the initial stage of a longitudinal study into the characterization of disease markers, GCF sampled from 104 sites in 74 adolescents was examined via sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS/PAGE). In this population, which had varying degrees of gingivitis but little evidence of destructive periodontitis, there was a highly homologous GCF protein profile. The plasma components, albumin, transferrin and IgG, were major constituents of all samples. In addition, a second group of non-plasma derived proteins, with molecular weights 37 kDa, 47 kDa, 57 kDa and 59 kDa, was also commonly detected. The high frequency of occurrence of these components suggests that they may represent products of normal turnover of the periodontal tissues. Analysis of GCF sampled from patients with progressing destructive disease revealed a different SDS/PAGE profile particularly with respect to proteins of non-plasma origin. It is anticipated that the major metabolic changes which accompany the destruction of the tissues during future disease episodes in the adolescent study population will be discernible as alterations to the GCF protein profile.

Detection of high-risk groups and individuals for periodontal diseases: laboratory markers from analysis of saliva

The use of saliva as a source of components that may identify subjects at risk of developing destructive periodontitis, or provide markers of disease potential or activity, has been reviewed. It was concluded that bacteria, their constituents or products are unlikely to be rewarding and that host-derived salivary factors such as enzymes cannot identify risk, as deficiency states for these do not exist. Secretory IgA, plasma IgA and IgG isotype levels and specific antibodies may be associated with risk, but probably only if levels fall below those which are protective or a specific antibody response is absent. More work is needed to distinguish between monomeric and dimeric IgA antibodies and to identify IgG antibodies in longitudinal clinical studies. In general, although saliva may prove to be useful as a source of indicators of current disease activity or as a means of assessing responses to treatment, it is unlikely to provide evidence for the existence of risk factors.

A method for the refinement of data arising from electrophoresis of biological fluids

Gingival crevicular fluid (GCF) is being analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) in our laboratory. We wish to characterize the major protein species in GCF and to investigate their association with the progression of disease. Laser densitometry of SDS/PAGE provides estimates of log molecular weight (LMW) and relative abundance for each band in each sample. Our aim was to develop a method for the refinement of these data into clusters which could be treated as distinct protein species, whose relation to disease progression could be assessed. A reproducibility study showed that the estimated LMW would fall within 3% of the true LMW 95% of the time. The method clusters the estimated LMWs of each band in each sample so that clusters form at LMWs which occurred frequently. The data from each band in each sample are thus refined into cluster number and relative abundance. Application of the technique to data from the reproducibility study showed that clusters formed around the individual components in the mixture, with little misclassification. The technique was then applied to two data sets: from SDS/PAGE of 104 GCF samples from 74 adolescents without progressive periodontal disease, and from 2 patients suffering from advanced progressive disease. The clusters appeared accurately to reflect the appearance of the gels, and clear differences were observed between the two data sets. The method will enable changes in the composition of biological fluids to be associated with external factors such as disease status and should be widely applicable.

Detection of high-risk groups and individuals for periodontal diseases: laboratory markers from analysis of gingival crevicular fluid

Gingival crevicular fluid is regarded as a promising medium for the detection of markers of periodontal diseases activity. The collection protocols are straight forward and non-invasive and can be performed at specific sites of interest in the periodontium. Because the fluid accumulates at the gingival margin, it will contain potential markers derived not only from the host tissues and serum but also the subgingival microbial plaque, and thus an extremely broad range of candidate molecules may be investigated. However, the ability to successfully describe indicators of current disease activity and predictors of future disease is dependent not only upon the choice of the biochemical marker but also on the accurate description of the health status of the sample sites using currently available clinical and radiographic methods. Areas of study which currently show the most promise involve the analysis of host enzyme activities directed against components of the extracellular matrix, the nature of the glycosaminoglycans released into the sulcus and the concentration in gingival crevicular fluid of certain mediators of the inflammatory process, most notably prostaglandin E2.

Detection of high-risk groups and individuals for periodontal diseases. Clinical assessment of the periodontium

The fundamental concepts of measuring periodontal diseases and the interpretation of such information as an historical record of disease, rather than disease activity, emphasises the need for improved diagnostic and prognostic tests. Criteria for an indicator of disease activity were suggested and an index fulfilling these should allow sites to be categorised as "active", quiescent or healing, and enable one to predict the risk of future disease activity. The ability of current measurements and indices, routinely used during clinical assessments of periodontal diseases, to fulfill the suggested criteria was considered and rejected in all cases. It is concluded that clinical parameters are only capable of identifying disease retrospectively, indicating the need for longitudinal, rather than cross-sectional studies in the search for clinical and laboratory markers of disease activity and susceptibility.

Detection of high-risk groups and individuals for periodontal diseases. Systemic predisposition and markers of general health

The evidence for systemic predisposition to periodontal diseases is reviewed in relation to cellular and humoral immunity, drug therapy, diet and nutrition and stress. It is concluded that, apart from defects of polymorphonuclear leukocytes (PMN) and Ehlers-Danlos Syndrome, little firm evidence exists for other diseases, though insulin-dependent diabetes and acquired immune deficiency syndrome (AIDS) may accelerate and/or potentiate the damage of existing disease. The precise rôle of drugs, diet and nutrition and stress remain to be elucidated, but recent advances in these areas offer the prospect of assessing risk using carefully controlled studies.

Detection of high-risk groups and individuals for periodontal diseases. Evidence for the existence of high-risk groups and individuals and approaches to their detection

It is argued that the periodontal diseases can no longer be regarded as universally prevalent conditions to which all members of the world's population are at equal risk if they fail to practise good oral hygiene. Rather, they should be regarded as a range of different diseases for each of which certain individuals, which together comprise certain minority groups, are at relatively high risk. The epidemiological evidence for the existence of high-risk groups is reviewed, from which it is concluded that world-wide the prevalence of severe destructive periodontitis is of the order of only 7-15% of the adult dentate population. A working classification of the different types of gingivitis and periodontitis is offered, as is a summary of the theoretically possible approaches to the detection of high-risk groups and individuals which are explored in detail in subsequent papers. Successful identification of such individuals will permit scientifically valid, rational and targetted prevention and treatment.