Those who work in any area of public health are exposed to large amounts of data and processed information. Some acquaintance with statistical methods can make that exposure more profitable. The objectives of this paper are to describe a suitable framework for governing scientific investigations which involve applied statistics, and to set down guidelines for research workers preparing material for publication. Final sections suggest further reading and give a brief description of some of the statistical software available to assist analysis.

Despite advances in health care in the tropics, and the inputs of international and voluntary organisations, famine and disaster continue to cause major devastation in many developing countries. In the aftermath of acute disasters such as earthquakes or cyclones and in chronic post-famine relief camps, mortality rates may be 20–30 times greater than those in ‘normal’ years [1]. The interaction of malnutrition, crowding, poor environmental sanitation, and changes in host parasite relationships due to migration or environmental change, result in communicable diseases playing a major role in excess morbidity and mortality.

Bacteriological quality of potable water supplying Morogoro municipality and its outskirts (population 135000 people) was assessed by the determination of the most probable number (MPN) of faecal coliforms, Escherichia coli, faecal streptococci and Clostridium perfringens for a period of 6 months. River water and chlorinated pipeborne water were found contaminated with microorganisms in the order of 3·8 x 101 to 4·95 x 103; 3·2 x 101 to 4·5 x 103; 101 to 6·4 x 101 and 1·2 x 101 to 2·5 x 102/100 ml of water respectively. Injured coliforms in treated water averaged 87 %. Pollution of river water by organic matter was much above acceptable standard. These findings indicate that there is a need for further treatment of water before consumption in order to avoid potential health hazards.

The use of ribosomal RNA (rRNA) gene restriction patterns to study the molecular epidemiology of Neisseria meningitidis was investigated. Ninety-four isolates of Neisseria meningitidis were characterized by their rRNA gene restriction patterns with 16 + 23 S rRNA from Escherichia coli as a probe. Thirteen rRNA gene restriction patterns were recognized; each of these patterns represented between 1 and 30 isolates. Isolates with the outbreak-associated phenotype B15P1.16 (sulphonamide resistant) all gave a single rRNA gene restriction pattern but this pattern also contained isolates with other phenotypes. Further discrimination between isolates was achieved by comparison of banding patterns resulting from restriction endonuclease digestion of chromosomal DNA with Bgl II. This gave a banding pattern consisting of about ten bands which was simple to interpret. Using this technique 94 isolates were classified in 54 patterns containing between 1 and 14 isolates. Restriction endonuclease analysis with Bgl II characterized outbreak-associated isolates with the phenotype B15P1.16 and enabled strains not typable by conventional methods to be identified as probable outbreak-associated isolates. The techniques should prove useful for epidemiological studies.

IN the first half of the year, 1941, an unusual number of cases of congenital cataract made their appearance in Sydney. Cases of similar type, which appeared during the same period, have since been reported from widely separated parts of Australia. Their frequency, unusual characteristics and wide distribution warranted closer investigation, and this report is an attempt to bring to notice some of the more important features of what might almost be regarded as a mild epidemic.

An outbreak of cryptosporidiosis resulted in 516 cases in Wiltshire and Oxfordshire. The outbreak caused widespread interest and led to an official inquiry. The majority of cases were in children; 8% of cases were admitted to hospital and the median duration of illness was 3 weeks. The geographical distribution of cases matched the distribution of water supplies from three treatment works and eryptosporidium oocysts were found at these works and in the treated water. Attack rates in electoral wards supplied by the three treatment works were significantly higher than in other wards. The cause of the outbreak appeared to be the failure of normal treatment to remove oocysts. Measures at the treatment works reduced the number of oocysts detected in treated water, after which the outbreak came to an end. The conclusion of the investigations was that cryptosporidiosis is a risk of conventionally treated public water supplies.

Fifty years ago in New South Wales the late Sir Norman Gregg [1] described congenital cataracts in 78 babies, 67 of whose mothers had had clinical rubella in early pregnancy; he concluded that the disease in the mother caused the abnormality in the baby. Gregg [1–3] and Swan [4, 5] and their colleagues reported that deafness, heart disease and microcephaly were also major components of the congenital rubella syndrome. The need to prevent this tragic outcome stimulated intensive work on laboratory diagnosis and vaccine development, leading to the isolation of rubella virus in 1962 and then to methods for antibody detection. These complementary advances established the two traditional pillars of virological diagnosis and opened the way to immunization, with the result that some countries are now on the verge of eliminating a disease which for over 100 years was regarded as no more than a mild and harmless exanthem of childhood.

Restriction digest fragments of DNA from 46 clinical isolates identified as Corynebacterium group D2, were separated by electrophoresis, Southern blotted onto nylon membranes and hybridized to a ribosomal RNA gene probe. The resulting band patterns were subjected to unweighed pair-group cluster analysis. Representative strains from the main clusters were compared with similarly prepared band patterns from type strains of human Corynebacterium species.

The results indicate that strains identified as Corynebacterium group D2 represent a unique taxon and that computer-assisted analysis of rRNA gene restriction fragment polymorphism (ribotyping) could be a useful technique in epidemiological studies of these bacteria.

Recovery from disseminated candidosis is associated with seroconversion to a 47 kDa breakdown product of the Heat Shock Protein (HSP) 90 of Candida albicans. Cloning, sequencing and epitope mapping has allowed the delineation of the immunodominant epitopes LKVIRKNIVKKMIE and STDEPAGESA. Monoclonal and polyclonal antibodies specific to these epitopes are used to show that all strains of C. albicans tested produce HSP 90 in both the yeast and mycelial phases. Homologous proteins are demonstrated in Saccharomyces cerevisiae, Candida parapsilosis and Corynebacterium jeikeium but not in Torulopsis glabrata. Evidence is presented for the existence of two distinct HSP 90s in C. albicans. The first of these is expressed constitutively whilst the second is produced on heat shocking the yeast from 23 to 37 °C.

The association between rubella in pregnancy and congenital anomalies was first reported 50 years ago, by N. McAlister Gregg, an Australian ophthalmologist [1]. During the next 20 years his findings were confirmed by others (reviewed in [2]). However, the first reports of the isolation of rubella virus in cell cultures and development of tests for neutralizing antibodies were not published until 1962 [3, 4]. Subsequent studies conducted in the UK and North America during a pandemic of rubella in 1963–4, were therefore able to make a more accurate estimate of the risks of maternal rubella at different stages of pregnancy. It was estimated that about 30000 rubella-damaged babies were born in the USA alone in 1963–4 [5]. This emphasized the importance of developing a vaccine to prevent infection in pregnancy and thereby, the birth of babies with rubella-induced congenital defects.

In August 1988 an increase was noted in the number of cases of cryptosporidiosis identified by the microbiology laboratory at Doncaster Royal Infirmary. By 31 October, 67 cases had been reported. Preliminary investigations implicated the use of one of two swimming pools at a local sports centre and oocysts were identified in the pool water. Inspection of the pool revealed significant plumbing defects which had allowed ingress of sewage from the main sewer into the circulating pool water. Epidemiological investigation confirmed an association between head immersion and illness. The pools were closed when oocysts were identified in the water and extensive cleaning and repair work was undertaken. The pool water was retested for cryptosporidial oocysts and found to be negative before the pool re-opened.

The first description of rubella in the UK was by an English physician, Dr William Maton, who reported an outbreak of an illness resembling a mild form of scarlatina in a boys' public school in 1815 [1]. Some years later, when observing the spread of a rash-associated illness in a large family, Maton described the characteristic clinical features of rubella, namely a mild prodromal illness followed by a generalized and often tingling rash lasting for a few days and associated with enlarged and tender glands in the occipital and postauricular regions. He also correctly identified the relatively long incubation period of rubella and noted the absence of fever and other signs of constitutional upset. Maton did not suggest an English name for this disease which had been previously described and called Rothëln by German physicians in the late 18th century. The term ‘rubella’ (Latin for ‘little red’) was first used in 1866 by another English physician, Dr Henry Veale, when describing an outbreak of Rothëln in a boys' school in India [2].

An enzyme-linked immunoassay (ELISA) has been developed to detect serum Immunoglobulin antibodies G and M to Treponema hyodysenteriae in vaccinated, experimentally infected and naturally infected swine. Naturally infected swine gave ELISA titres that were similar to experimentally infected swine, but were significantly less than the titres of vaccinated swine. When serum from naturally infected swine was used to probe nitrocellulose blots of sodium dodecyl sulphate–polyacrylamide gel electrophoresed whole cell proteins of T. hyodysenteriae, the immunoblotting patterns showed IgG antibodies were produced against many T. hyodysenteriae protein antigens and against lipopolysaccharide (LPS). The IgG antibodies directed against LPS were serotype-specific for that LPS and could be used to identify the serotype involved in the T. hyodysenteriae infection in that herd. IgM immunoblots also reacted with the many protein antigens but were less specific for LPS antigen, with a substantial degree of crossreaction between the LPS of all serotypes.

The data demonstrate that a microplate enzyme-linked immunosorbent assay, coupled with immunoblotting, is a very specific and sensitive test for detection of antibody to Treponema hyodysenteriae in swine.

An outbreak of cryptosporidiosis occurred in the Isle of Thanet during December 1990 and January 1991. A total of 47 cases ranging in age from 2 months to 85 years were identified in residents from the Margate, Broadstairs and Ramsgate areas, with dates of onset of illness from 3 December to 14 January. A case-control study demonstrated a strong statistical association between illness and the consumption of unboiled tap water from a particular source, with evidence of a dose–response relationship. Although no cryptosporidial oocysts were identified in samples of untreated or treated water taken during the investigation, the results were consistent with the view that the source of infection was treated river water which was used to supplement borehole water.

DNA- fingerprints (Hind III) of Streptococcus uberis field isolates from New York State and Europe showed substantial homogeneity, but were different to those of the type strain of the newly proposed psychrophilic species S. parauberis. S. uberis strains had major SDS-heat extracted antigens of molecular masses (Mr) < 14, 40–41, 42–43, 59–61, 80–86 and 118–122 kDa following immunoblotting with rabbit hyperimmune sera. Bovine sera and milk reacted with the 40–41 and 118–122 kDa antigens. Variations in the Mr of particular bands were too unevenly distributed to permit formation of subgroups. Although cross reactive, the sizes of the antigens of S. parauberis strain NCDO 2020 were substantially different to those of S. uberis, the most prominent antigen having a Mr of 50 kDa. The antigenic and genetic data therefore strongly support the introduction of S. parauberis as a distinct species. S. uberis strains reacted with antiserum to Lancefield groups B, E, G and P, their grouping reactions showing no correlation with DNA and immunoblot fingerprints. Lancefield grouping of S. uberis therefore appears to have little value in identification.

Environmental contamination has been shown to be an important aspect of the epidemiology of salmonellosis in calves. Markets and transport vehicles are important links in the calf marketing chain and these were investigated to determine the level of salmonella contamination.

Salmonellas were isolated from 7 of the 14 markets surveyed, with 31 of 838 samples (3.7%) being positive. Nine different salmonella serotypes, of which the commonest was Salmonella typhimurium, were isolated. Four different phage types of S. typhimurium were detected, the commonest being DT204C.

Salmonellas were isolated from 22 of the 107 vehicles (20.6%) examined before washing and from 4 of the 62 vehicles (6.5%) examined after cleaning. Twelve different salmonella serotypes were isolated, of which the most frequent was S. typhimurium. The commonest of the six different S. typhimurium phage types was DT204C.

These results indicate that improved cleaning and disinfection routines both for vehicles and markets are necessary to control salmonellosis in calves.

Postnatal rubella is a mild illness, a disease which was considered to be of only minor importance for many years. The first authors to write about the disease as distinct from other exanthemata were German physicians; they differentiated rubella from measles and scarlet fever in the latter part of the eighteenth century and called the disease Rotheln. Hence the common English language eponym is ‘German measles’. Some consider that the term ‘German’ in German measles is probably of literary rather than of geographical significance and that it came from the old French ‘germain’ (derived from the Latin ‘germanus‘), meaning ‘closely akin to’ measles [1]. That it is not generally called by its German name, Rotheln, is due to Veale, a Scottish physician who in 1866 described 30 cases of rubella in the Edinburgh Medical Journal, and proposed ‘rubella’ as a short and euphonius name that could be easily pronounced [2].

More than 25 years have passed since the last rubella epidemic in the United States. The rubella pandemic of 1964–5 demonstrated clearly the extraordinary teratogenic potential of the rubella virus. In the United States alone, it is estimated that more than 12500000 cases of rubella occurred during the winter and spring of 1964–5. Congenital rubella infection occurred in an estimated 30000 pregnancies, 10000 resulting in fetal death or therapeutic abortion and 20000 resulting in infants born with congenital rubella syndrome (CRS) [1]. In contrast, during 1988, only 225 cases of rubella were reported to the Centers for Disease Control (CDC) in Atlanta, the lowest annual total since rubella became a nationally notifiable disease in 1966 [2]. However, in 1989, this downward trend of reported cases was interrupted, with the number of reported rubella cases in the United States increasing nearly twofold, and in 1990, the total increased another threefold (to more than 1000 cases) [3]. Although the 1990 reports represent the highest total since 1982, the overall incidence of rubella in the United States has still declined by more than 98% since 1969, the year rubella vaccine was licensed (Fig. 1).

The diagnosis of maternal infection in early pregnancy depends on tests which are sensitive to recent infection, such as specific IgM. Two types of test are considered: those where the response persists for a period following infection and then declines, such as IgM. and those whose response increases with time since infection, such as IgG-avidity. However, individuals vary in their response to infection, and it may not always be possible to determine whether an infection occurred during pregnancy or before it. Mathematical methods are developed to evaluate the performance of these tests, and are applied to the diagnosis of toxoplasmosis in pregnancy. It is shown that, based on existing information, tests of recent infection are unlikely to be both sensitive and predictive. More data on these tests are required, before they can be reliably used to determine whether infection has occurred during pregnancy or before it.