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The clinical manifestations of infection were analysed during an outbreak of 34 cases ofYersinia pseudotuberculosis serotype Ia infection. The diagnosis was based on the results of enzyme immunoassay and verified by stool culture in five cases. The first four patients were pupils from the same school, and information on any signs and symptoms of infection was obtained by questionnaire from pupils of the school. A blood sample was obtained from 101 children. Strong IgM and IgG antibody responses toYersinia pseudotuberculosis Ia were found in 13 (25%) of the 52 pupils who reported signs and symptoms of infection and in 9 (18%) of the 49 with no manifestations of infection. The vigorous immune response also resulted in effective opsonization of the causative microorganism. The most common symptoms were fever and abdominal pain. Three children operated on because of suspected appendicitis were found to have mesenteric lymphadenitis. Only one patient developed reactive arthritis. Analysis showed that a remarkable proportion ofYersinia pseudotuberculosis infections may be subclinical, and that individualYersinia pseudotuberculosis strains may have different capacities to cause postinfection complications.

The polymorphonuclear leukocyte (PMN) chemiluminescence (CL) response to opsonized zymosan reflecting the C3b/C3bi-receptor-mediated PMN respiratory burst activation was studied in 99 arthritic patients typed for the HLA-B27 antigen. The results indicate that the B27 antigen per se is not associated with disturbances in PMN CL response. However, the erythrocyte sedimentation rate showed a correlation with CL, suggesting that the activity of arthritic disease may affect the PMN CL response.

The interaction between fibronectin and Yersinia strains was studied. Wild-type Y. enterocolitica strains expressing the virulence-plasmid-encoded adhesion protein YadA adhered strongly to fibronectin-coated coverslips, while their plasmid-cured variants expressed weaker binding. The cloned yadA gene of Y. enterocolitica or Y. pseudotuberculosis conferred fibronectin-binding ability both to Escherichia coli and to Y. psuedotuberculosis strains lacking the YadA protein. The YadA protein did not mediate binding to isolated fragments of fibronectin or to soluble fibronectin.

We have determined the opsonic capacity of specific antibodies in patient sera obtained after Yersinia infection. The results indicate that Yersinia antibodies lead to complement activation through the classical pathway, thus overcoming the inhibition of complement-mediated opsonization in the absence of specific antibodies provided by the virulence plasmid in Yersinia enterocolitica and Yersinia pseudotuberculosis. Further, antibodies against plasmid-encoded structures, the Yersinia outer membrane proteins (YOPs), are not necessary in this effect. This is indicated by two facts. (i) Monoclonal antibodies directed against the O polysaccharide of Y. enterocolitica O:3 are capable of opsonizing the plasmid-containing bacteria through C1q binding. (ii) Rabbit antisera show opsonic activity when obtained by immunization both with plasmid-containing Y. enterocolitica expressing the YOPs and a plasmid-cured variant not expressing these proteins.

In this study we evaluated secretor status in patients with reactive arthritis. Previous evidence indicates that non-secretion of ABO and Lewis blood group antigens to saliva and other secretions is associated with susceptibility to certain bacterial infections and certain diseases with suspected autoimmune etiology. Secretor status can be determined based on the Lewis phenotype. We studied ABO, Lewis and Rhesus blood groups of 54 patients with previous reactive arthritis, 26 of whom had uroarthritis and 28 of whom had arthritis after enteric infection. Furthermore, 25 patients with uncomplicated yersiniosis and 57 healthy controls were studied. We did not find any correlation between secretor status and reactive arthritis or gastroenteritis due to Yersinia. ABO blood group antigen B appeared to be protective against uroarthritis.

An outbreak of Yersinia pseudotuberculosis serotype III infection in Turku, Finland, is described. The strain had not been encountered in the area earlier. In detecting the outbreak, the bacteriological identification of the atypical strain and rapid development of serological diagnostics (E1A) were decisive. Altogether 19 cases were found. In spite of extensive studies, no transmitting factor could be detected. The serological response of the patients was unusually slow and weak in some cases. Interestingly, the incidence of postinfectious complications was quite high. Six patients had erythema nodosum, four had reactive arthritis, one had iritis and one had mild nephritis; altogether 10 patients out of 19 developed complications. The outbreak demonstrates that some Yersinia strains may have special capacity to induce postinfectious complications.

Phagocytosis provides one of the body's first-line defences against invading bacteria. The present study evaluated granulocyte microbicidal-related oxidative mechanisms by measurement of chem-iluminescence responses in the phagocytosis of zymosan, S. aureus, E. coli and N-formyl-methionyl-leucylphenylalanine (FMLP) in 12 patients undergoing coronary bypass surgery under high-dose fentanyl anaesthesia. With preoperative values as a baseline, a significant depression of in vitro responses to zymosan was seen on days 1, 3–4 after operation and to S. aureus and E. coli on days 3–4 after operation, with recovery by days 6–7. Responses to FMLP were unaffected.

Nineteen patients were involved in an outbreak of infection caused by Yersinia pseudotuberculosis serotype 3. No epidemics attributable to this microorganism have been previously reported; the most extensive known cluster of cases involved four children in one family and their pet dog. The key finding in the outbreak described in the present study was the bacteriologic identification of serotype 3 in stool specimens from patients with clinically typical yersiniosis. Twelve cases were identified by isolation of Y pseudotuberculosis from stool specimens. An ELISA permitted serological diagnosis of the remaining seven cases. The antibody response was unusually slow in some patients. A noteworthy feature of the outbreak was the high incidence of postinfection complications, which developed in 10 of 19 patients. In spite of active screening of the respective families and environments of the patients, no transmitting factor was found, and the precise source of the infection remains unknown.