It might seem very late to suggest, nearly 400 years after the first clinical description of influenza and 54 years after its isolation (reviewed by Stuart-Harris. Schild & Oxford, 1985), that many fundamental questions remain to be answered about the virus itself. However the precise antigenic and biochemical structure of the natural field virus has not been established. If so much remains to be learned concerning the nature of the virion then perhaps it may be less surprising that there are some conflicting theories as regards influenza epidemiology. Such questions are raised in the current volume of the journal where Hope-Simpson & Golubev (pp. 5 54) propose a major role for virus persistence in the human disease and, a lesser role for a linked chain of acute infection spreading influenza around the world (see also Hope-Simpson. 1979: 1981). This would be a minority view of the epidemiology of influenza A at present and is most definitely in conflict with the orthodox idea of person to person spread in an endless chain.

Influenza A virus was discovered in 1933, and since then four major variants have caused all the epidemies of human influenza A. Each had an era of solo world prevalence until 1977 as follows: H0N1 (old style) strains until 1946. H1N1 (old style) strains until 1957, H2N2 strains until 1968. then H3N2 strains, which were joined in 1977 by a renewed prevalence of H1N1 (old style) strains.

Serological studies show that H2N2 strains probably had had a previous era of world prevalence during the last quarter of the nineteenth century, and had then been replaced by H3N2 strains from about 1900 to 1918. From about 1907 the H3N2 strains had been joined, as now. by H1N1 (old style) strains until both had been replaced in 1918 by a fifth major variant closely related to swine influenza virus A/Hswine1N1 (old style), which had then had an era of solo world prevalence in mankind until about 1929. when it had been replaced by the H0N1 strains that were first isolated in 1933.

Eras of prevalence of a major variant have usually been initiated by a severe pandemic followed at intervals of a year or two by successive epidemics in each of which the nature of the virus is usually a little changed (antigenic drift), but not enough to permit frequent recurrent infections during the same era. Changes of major variant (antigenic shift) are large enough to permit reinfection. At both major and minor changes the strains of the previous variant tend to disappear and to be replaced within a single season, worldwide in the case of a major variant, or in the area of prevalence of a previous minor variant.

Pandemics, epidemics and antigenic variations all occur seasonally, and influenza and its viruses virtually disappear from the population of any locality between epidemics, an interval of many consecutive months. A global view, however, shows influenza continually present in the world population, progressing each year south and then north, thus crossing the equator twice yearly around the equinoxes, the tropical monsoon periods. Influenza arrives in the temperate latitudes in the colder months, about 6 months separating its arrival in the two hemispheres.

None of this behaviour is explained by the current concept that the virus is surviving like measles virus by direct spread from the sick providing endless chains of human influenza A. A number of other aspects of the human host influenza A virus relationship encountered in household outbreaks are among the list of 20 difficulties that are inexplicable by the current concept of direct spread.

Alternative concepts have usually been designed to counter particular difficulties and are incompatible with other features of influenzal behaviour in mankind. The new concept detailed in the appendix provides simple explanations for most if not all of the difficulties. It proposes that influenza A virus cannot normally be transmitted during the illness because it too rapidly becomes non-infectious in a mode of persistence or latency in the human host. Many months or a year or two later it is reactivated by a seasonally mediated stimulus which, like all seasonal phenomena, is ultimately dependent on variations in solar radiation caused by the tilt of the plane of earth's rotation in relation to that of its circumsolar orbit. The carriers, who are always widely seeded throughout the world population, become briefly infectious and their non-immune companions, if infected, comprise the whole of the next epidemic. The reactivated virus particles must encounter the immunity they have engendered in the carrier, thus allowing minor mutants an advantage over virions identical with the parent virus, and so favouring antigenic drift and automatic disappearance of predecessor and prompt seasonal replacement. Antigenic shift and recycling of major variants may also be explained by virus latency in the human host.

Enzyme immunoassays (EIA) for IgG and IgM antibodies against influenza A and B virus are described. One hundred and seven subjects with a clinical diagnosis of acute respiratory infection (influenza, bronchitis or pneumonia) were selected for this study during two epidemics of influenza A which occurred in Finland in 1983 and 1985. Paired sera and nasopharyngeal secretions were obtained from all subjects. The sera were tested for influenza A and B antibodies by IgG and IgM EIAs and by complement fixation tests. The nasopharyngeal secretions were tested by an indirect EIA for influenza A and B antigens.

The IgG EIA was found to be better than complement fixation for the diagnosis of influenza A infections: only 22% of the significant increases detected by this test were also positive by complement fixation. The additional contribution of the IgM EIA to the number of positives was minimal.

It was also found that testing a single 1/1000 dilution of serum for influenza A and 1/100 dilution for influenza B in the IgG EIA gave as many positives as the conventional method of testing several dilutions.

Mathematical models and statistical analyses of epidemiological data are employed to assess the potential impact of mass vaccination on the incidences of cases of mumps infection and cases of mumps related complications. The analyses reveal that in the United Kingdom the average age at infection with the mumps virus is currently between 6–7 years and that the inter-epidemic period of the infection is approximately 3 years. The critical level of vaccine uptake to eliminate mumps virus transmission is predicted to be approximately 85% of each cohort of boys and girls by the age of 2 years. Analyses of published data show that the risk of complication arising from mumps infection is markedly age- and sex-related. Model predictions suggest that the incidence of orchitis will be increased, over the level pertaining prior to mass vaccination, by levels of vaccine uptake (by 2 years of age) that are less than 70% of each yearly cohort of boys and girls. Moderate (over 00%) to high (75%) levels of vaccine uptake, however, are predicted to reduce the overall incidence of cases of mumps related complications (especially those with CNS involvement).

This study compares the presence and level of measles haemagglutination inhibiting antibody in the sera of primary school children in selected rural and urban areas of Kaduna State, Nigeria following a vaccination campaign. The results, analysed by Mann-Whitney statistical test at α=0·05, showed significantly higher levels of haemagglutination inhibiting antibody in all the age groups in urban areas when compared with rural areas. The implications of these findings on measles vaccination campaigns are discussed.

In 1978, 22 staff members of the National Institute of Virology, Pune, India, were given two doses of human diploid cell antirabies vaccine (HDCV) for primary pre-exposure prophylactic immunization; the interval between the two doses being approximately 4 weeks. Eighteen of these 22 vaccinees were given a booster dose 1 year later. All 18 vaccinees developed protective levels of antibody; most of them had antibody levels exceeding 10 IU/ml.

In 1984, 5 years after the booster dose, 11 (79·0%) of 14 vaccinees tested still possessed neutralizing antibody levels ranging from 0·5 IU/ml to 10 IU/ml. Fourteen days after the administration of a booster dose, the antibody levels ranged from 10 to ≥ 100 IU/ml for all except one vaccinee (5·2 IU/ml). These findings demonstrate that the majority of vaccinees retained detectable neutralizing antibody after pre-exposure prophylaxis for as long as 5 years and that a single booster dose thereafter evoked a good antibody response.

In 1962 the Public Health Laboratory Service (PHLS) became responsible for the Poliomyelitis Surveillance Scheme for England and Wales, which since 1970 has included the World Health Organisation (WHO) enquiry into Acute Persisting Spinal Paralysis. All the records have been kept, including those of patients who were later considered not to have had poliomyelitis. This paper reviews the cases between 1970–84 of patients normally resident in England and Wales, where the clinical features of the illness were considered by the clinician in charge to be those of poliomyelitis and in which either poliovirus was isolated or there was serological evidence of recent infection. Seventy cases met these criteria. Two patients died. A wild strain of poliovirus was isolated in 19 cases; a vaccine-like strain in 27; an intermediate strain in 5; and in 19 cases the strain was not known or there was no isolate. Eleven patients had a history of overseas travel; 17 had been vaccinated recently; and 12 had been in contact with a recent vaccinee. In the remaining 30 cases, the source of the infection was not found. Other details, including the age distribution, vaccination history and the laboratory findings are discussed.

Twelve British isolates of leptospira belonging to the Sejroe serogroup were examined using a series of six factor sera prepared by a number of different absorption methods. Ten of the isolates were identified as Leptospira interrogans serovar hardjo and two as L. interrogans serovar saxkoebing. These isolates had previously been identified using the cross agglutination absorption method.

Some 94 strains of Ieptospires belonging to the Sejroe serogroup isolated in the British Isles were identified to the serovar level using specific factor sera.

Seventy strains were identified as Leptospira interrogans serovar hardjo, 66 from cattle, 2 from pigs and 1 each from a sheep foetus and a human.

Twenty-four strains were identified as L. interrogans serovar saxkoebing, most strains were isolated from either wood mice, bank or field voles but strains were also isolated from badgers, a fox and a dog.

A total of 91 food and environmental samples were examined for the presence of salmonollao using a commercially available enzyme immunoassay kit (EIA) and a conventional culture technique. A 78% agreement was obtained, but re-examination of culture-negative, EIA-positive samples gave agreement of 86%. The problem of comparing EIA and culture results is discussed. A partially selective pre-enrichment broth was tested in 37 samples and gave better EIA ratios. Artificially contaminated cooked foods gave 100% agreement.

Isolates of Salmonella typhimurium, recovered over a 9-month period from a child with gastroenteritis, were characterized by biotyping, phage-typing and plasmid-profile analysis. Because the data from the different methods were discrepant, it was difficult to establish whether her infection was due to a single strain that had changed character in vivo or was due to recurrent infections with different, unrelated strains. Restriction-enzyme fingerprinting of the plasmids from the different isolates provided an explanation for the initial discrepancy and highlighted a source of potential confusion in epidemiological studies.

A total of 308 samples of different types were examined for the presence of salmonellas by means of three different procedures. The first consisted of preenrichment in buffered peptone water followed by enrichment in Rappaport-Vassiliadis medium (P/RV). The second differed only in that 1% Teepol was added to the pre-enrichment medium (PT/RV). In the third, buffered peptone water with 1% Teepol was followed by enrichment in Muller–Kauffmann tetrathionate broth also containing 1% Teepol (PT/MKT). The first of these combinations (P/RV) proved superior to the others both in terms of isolation rates and in the appearance of suspicious colonies.

Attempts were made to discover the source of strains of haemolytic Escherichia coli infecting weaned pigs on a piggery. The organisms were not detected in the faeces of sows in the farrowing house, or in the in the faeces or intestinal tracts of slaughtered bacon pigs or sows. Sows held in a quarantine unit, and their offspring born in the unit, did not excrete haemolytic E. coli until after they were returned to the piggery.

The environment of the piggery was the most likely source of infection for weaned pigs, and routine cleaning and disinfection of the accommodation did not prevent infection. Unweaned pigs were however able to transfer haemolytic E. coli to a newly built, previously unused weaning house, and establish a cycle of infection.

Two single-tube media, lactose-tryptone-lauryl sulphate broth (LTLSB) and lauryl-tryptose-mannitol broth were tested in parallel in a series of 1111 tests on water samples from a variety of sources.

LTLSB was found to be superior both in gas and indole production from Escherichia coli when incubated at 44 °C and is recommended as the most suitable single-tube confirmatory test for this organism.

Following isolation of Legionella pneumophila from a special dental station water circuit, used primarily to cool high-speed dental drills which produce fine aerosols, a case finding and environmental survey was undertaken. Widespread colonization of the dental stations was found and the results suggested that amplification of the background levels of L. pneumophila was taking place within the stations. However there was no evidence for transmission causing human infection.

Food poisoning caused by Clostridium botulinum toxin A occurred in Japan. Eleven (31 %) of 36 patients from 14 different areas died of botulism. Most of the patients had eaten commercial fried lotus-rhizome solid mustard without heating. The food, which implicated one of the special local products used for gifts in Kumamoto, was found to have been produced by a manufacturer in Kumamoto prefecture.

In Fukuoka prefecture, two of three patients died on days 4 and 8 after eating the food; they had typical symptoms of botulism. A total of 42 packages of the food bought as gifts was collected from different districts in Fukuoka prefecture for examination for both organism and toxin. Thirteen of these (31%) were contaminated with the organism, and in 11 (26%) a small amount of toxin A had been produced.

The herd incidence of confirmed Mycobacterium bovis infection in cattle in the south-west of England has been approximately ten times that of the remainder of England and Wales; this greater incidence has been attributed to infection from badgers. The incidence of herds with only non-visible lesioned tuberculin test reactors, from which M. bovis was not isolated, has also remained higherin the south-west region.

The incidences of these latter unconfirmed incidents were compared in parishes in the south-west region in which M. bovis in cattle had been confirmed, and those where M. bovis had not been confirmed, for the period 1979–83. This analysis was carried out both for those parishes in which herds had been subjected to annual tuberculin testing and for those subjected to biennial tuberculin testing. The incidence of unconfirmed incidents was significantly higher in parishes in which confirmedincidents had occurred, and this difference was found in both the annual and biennially tested parishes. The relative risks for the incidence of unconfirmed incidents in annually and biennially tested parishes were 1*89 and 2–56, respectively. The incidence of unconfirmed incidents in biennially tested parishes was lower than in annually tested parishes.

The incidence of non-specific tuberculin test reactor herds was estimated from tuberculin test results in the eastern region of England during a period when tuberculosis was not confirmed in cattle. A comparison of this incidence and that of unconfirmed incidents in the south-west region suggests that approximately 70% of the unconfirmed incidents in the south-west were related to exposure to M. bovis.

The results of the analyses indicate that unconfirmed incidents cannot be completely ignored in epidemiological analyses and studies of bovine tuberculosis in the problem areas of the south-west region of England.

Strains of Haemophilus influenzae isolated from patients in N.E. Scotland between 1983 and 1986 have been subtyped by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell polypeptides. Gels were stained with Coomassie blue and polypeptide profiles were analysed using the Dice coefficient of similarity.

Type b strains were all closely related, the 19 strains analysed being grouped at a 90% similarity level into one large (13 strains) and one small (3 strains) cluster with 3 strains being ungrouped. Thirty-six non-typable, epidemiologically unrelated strains were subtyped; one pair of strains had indistinguishable polypeptide profiles. The polypeptide profiles of the remaining strains showed much heterogeneity, although groups of strains isolated from the same patient over short periods showed indistinguishable profiles.

A high percentage of non-typable (NT) Staphylococcus aureus strains was isolated in Spanish hospitals during 1984 and 1985. Several alternative methods of typing were employed to study these isolates. These were: phage-typing at 1000 × RTD, phage-typing after heat-treatment (48 °C), thermal shock (56 °C), reverse-typing and induction of additional phages. Using these methods the number of NT isolates was reducedby 60%. Best results were obtained with heat-treatment. Additional phages and reverse-typing were also useful.

A scheme for the study of outbreaks and sporadic cases caused by NT strains is proposed using the methods described.

Candida albicans has recently been described as a cause of nosocomial infection. This paper reports four further outbreaks occurring over a 12-month period in England. There were 13 systemic cases and 6 deaths. The outbreaks were defined by morphotyping andthe new technique of immunoblot fingerprinting. Controi of the outbreaks was produced bythe implementation of strict cross-infection control policies without recourse to systemic chemoprophylaxis.