Representativeness, Vaccination Uptake, and COVID-19 Clinical Outcomes 2020-2021 in the UK Oxford-Royal College of General Practitioners Research and Surveillance Network: Cohort Profile Summary

BACKGROUND

The Oxford-Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) is one of Europe's oldest sentinel systems, working with the UK Health Security Agency (UKHSA) and its predecessor bodies for 55 years. Its surveillance report now runs twice weekly, supplemented by online observatories. In addition to conducting sentinel surveillance from a nationally representative group of practices, the RSC is now also providing data for syndromic surveillance.

OBJECTIVE

The aim of this study was to describe the cohort profile at the start of the 2021-2022 surveillance season and recent changes to our surveillance practice.

METHODS

The RSC's pseudonymized primary care data, linked to hospital and other data, are held in the Oxford-RCGP Clinical Informatics Digital Hub, a Trusted Research Environment. We describe the RSC's cohort profile as of September 2021, divided into a Primary Care Sentinel Cohort (PCSC)-collecting virological and serological specimens-and a larger group of syndromic surveillance general practices (SSGPs). We report changes to our sampling strategy that brings the RSC into alignment with European Centre for Disease Control guidance and then compare our cohort's sociodemographic characteristics with Office for National Statistics data. We further describe influenza and COVID-19 vaccine coverage for the 2020-2021 season (week 40 of 2020 to week 39 of 2021), with the latter differentiated by vaccine brand. Finally, we report COVID-19-related outcomes in terms of hospitalization, intensive care unit (ICU) admission, and death.

RESULTS

As a response to COVID-19, the RSC grew from just over 500 PCSC practices in 2019 to 1879 practices in 2021 (PCSC, n=938; SSGP, n=1203). This represents 28.6% of English general practices and 30.59% (17,299,780/56,550,136) of the population. In the reporting period, the PCSC collected >8000 virology and >23,000 serology samples. The RSC population was broadly representative of the national population in terms of age, gender, ethnicity, National Health Service Region, socioeconomic status, obesity, and smoking habit. The RSC captured vaccine coverage data for influenza (n=5.4 million) and COVID-19, reporting dose one (n=11.9 million), two (n=11 million), and three (n=0.4 million) for the latter as well as brand-specific uptake data (AstraZeneca vaccine, n=11.6 million; Pfizer, n=10.8 million; and Moderna, n=0.7 million). The median (IQR) number of COVID-19 hospitalizations and ICU admissions was 1181 (559-1559) and 115 (50-174) per week, respectively.

CONCLUSIONS

The RSC is broadly representative of the national population; its PCSC is geographically representative and its SSGPs are newly supporting UKHSA syndromic surveillance efforts. The network captures vaccine coverage and has expanded from reporting primary care attendances to providing data on onward hospital outcomes and deaths. The challenge remains to increase virological and serological sampling to monitor the effectiveness and waning of all vaccines available in a timely manner.

Pfizer-BioNTech and Oxford AstraZeneca COVID-19 vaccine effectiveness and immune response among individuals in clinical risk groups

Background COVID-19 vaccines approved in the UK are highly effective in general population cohorts, however, data on effectiveness amongst individuals with clinical conditions that place them at increased risk of severe disease are limited.

Methods We used GP electronic health record data, sentinel virology swabbing and antibody testing within a cohort of 712 general practices across England to estimate vaccine antibody response and vaccine effectiveness against medically attended COVID-19 amongst individuals in clinical risk groups using cohort and test-negative case control designs.

Findings There was no reduction in S-antibody positivity in most clinical risk groups, however reduced S-antibody positivity and response was significant in the immunosuppressed group. Reduced vaccine effectiveness against clinical disease was also noted in the immunosuppressed group; after a second dose, effectiveness was moderate (Pfizer: 59.6%, 95%CI 18.0–80.1%; AstraZeneca 60.0%, 95%CI -63.6–90.2%).

Interpretation In most clinical risk groups, immune response to primary vaccination was maintained and high levels of vaccine effectiveness were seen. Reduced antibody response and vaccine effectiveness were seen after 1 dose of vaccine amongst a broad immunosuppressed group, and second dose vaccine effectiveness was moderate. These findings support maximising coverage in immunosuppressed individuals and the policy of prioritisation of this group for third doses.

Interim findings from first-dose mass COVID-19 vaccination roll-out and COVID-19 hospital admissions in Scotland: a national prospective cohort study

BACKGROUND

The BNT162b2 mRNA (Pfizer-BioNTech) and ChAdOx1 nCoV-19 (Oxford-AstraZeneca) COVID-19 vaccines have shown high efficacy against disease in phase 3 clinical trials and are now being used in national vaccination programmes in the UK and several other countries. Studying the real-world effects of these vaccines is an urgent requirement. The aim of our study was to investigate the association between the mass roll-out of the first doses of these COVID-19 vaccines and hospital admissions for COVID-19.

METHODS

We did a prospective cohort study using the Early Pandemic Evaluation and Enhanced Surveillance of COVID-19-EAVE II-database comprising linked vaccination, primary care, real-time reverse transcription-PCR testing, and hospital admission patient records for 5·4 million people in Scotland (about 99% of the population) registered at 940 general practices. Individuals who had previously tested positive were excluded from the analysis. A time-dependent Cox model and Poisson regression models with inverse propensity weights were fitted to estimate effectiveness against COVID-19 hospital admission (defined as 1-adjusted rate ratio) following the first dose of vaccine.

FINDINGS

Between Dec 8, 2020, and Feb 22, 2021, a total of 1 331 993 people were vaccinated over the study period. The mean age of those vaccinated was 65·0 years (SD 16·2). The first dose of the BNT162b2 mRNA vaccine was associated with a vaccine effect of 91% (95% CI 85-94) for reduced COVID-19 hospital admission at 28-34 days post-vaccination. Vaccine effect at the same time interval for the ChAdOx1 vaccine was 88% (95% CI 75-94). Results of combined vaccine effects against hospital admission due to COVID-19 were similar when restricting the analysis to those aged 80 years and older (83%, 95% CI 72-89 at 28-34 days post-vaccination).

INTERPRETATION

Mass roll-out of the first doses of the BNT162b2 mRNA and ChAdOx1 vaccines was associated with substantial reductions in the risk of hospital admission due to COVID-19 in Scotland. There remains the possibility that some of the observed effects might have been due to residual confounding.

FUNDING

UK Research and Innovation (Medical Research Council), Research and Innovation Industrial Strategy Challenge Fund, Health Data Research UK.

Interim findings from first-dose mass COVID-19 vaccination roll-out and COVID-19 hospital admissions in Scotland: a national prospective cohort study

BACKGROUND

The BNT162b2 mRNA (Pfizer-BioNTech) and ChAdOx1 nCoV-19 (Oxford-AstraZeneca) COVID-19 vaccines have shown high efficacy against disease in phase 3 clinical trials and are now being used in national vaccination programmes in the UK and several other countries. Studying the real-world effects of these vaccines is an urgent requirement. The aim of our study was to investigate the association between the mass roll-out of the first doses of these COVID-19 vaccines and hospital admissions for COVID-19.

METHODS

We did a prospective cohort study using the Early Pandemic Evaluation and Enhanced Surveillance of COVID-19-EAVE II-database comprising linked vaccination, primary care, real-time reverse transcription-PCR testing, and hospital admission patient records for 5·4 million people in Scotland (about 99% of the population) registered at 940 general practices. Individuals who had previously tested positive were excluded from the analysis. A time-dependent Cox model and Poisson regression models with inverse propensity weights were fitted to estimate effectiveness against COVID-19 hospital admission (defined as 1-adjusted rate ratio) following the first dose of vaccine.

FINDINGS

Between Dec 8, 2020, and Feb 22, 2021, a total of 1 331 993 people were vaccinated over the study period. The mean age of those vaccinated was 65·0 years (SD 16·2). The first dose of the BNT162b2 mRNA vaccine was associated with a vaccine effect of 91% (95% CI 85-94) for reduced COVID-19 hospital admission at 28-34 days post-vaccination. Vaccine effect at the same time interval for the ChAdOx1 vaccine was 88% (95% CI 75-94). Results of combined vaccine effects against hospital admission due to COVID-19 were similar when restricting the analysis to those aged 80 years and older (83%, 95% CI 72-89 at 28-34 days post-vaccination).

INTERPRETATION

Mass roll-out of the first doses of the BNT162b2 mRNA and ChAdOx1 vaccines was associated with substantial reductions in the risk of hospital admission due to COVID-19 in Scotland. There remains the possibility that some of the observed effects might have been due to residual confounding.

FUNDING

UK Research and Innovation (Medical Research Council), Research and Innovation Industrial Strategy Challenge Fund, Health Data Research UK.

Increase in ST-11 serogroup W Neisseria meningitidis invasive meningococcal disease in Canada, 2016-2018

BACKGROUND

Many countries have experienced increases in invasive meningococcal disease (IMD) due to a serogroup W Neisseria meningitidis (MenW) strain of the multilocus sequence type (ST)-11 clonal complex (CC). MenW ST-11 was first reported in Ontario, Canada, in 2014. By 2016, this strain caused IMD in five provinces and was responsible for 18.8% of the IMD cases in Canada.

OBJECTIVE

To provide an update on invasive MenW disease in Canada including the strain characteristics, specimen source of isolates, age, sex and geographic distribution of cases.

METHODS

N. meningitidis from culture-positive IMD cases are routinely submitted to the National Microbiology Laboratory (NML) for serogroup, serotype, serosubtype and sequence type analysis. The data from January 1, 2016 to December 31, 2018 were analyzed by calculating the proportion of IMD cases caused by MenW compared with other serogroups. In addition, trends based on age, sex and geographic distribution of cases and specimen source of isolates were analyzed based on information on specimen requisition forms.

RESULTS

Over the 3-year period, 292 individual IMD case isolates were analyzed. The percentage of IMD case isolates typed as MenW more than doubled from 19% (n=15) to 44% (n=51) in 2018 when MenW became the most common serogroup, exceeded the number of MenB, MenC or MenY. In total, 93 MenW case isolates were identified, 91% (n=85) belonged to the ST-11 CC. The increase in MenW affected all age groups (but was most common in those older than 60) and both sexes, and occurred across the country but most prevalent in western Canada. The most common specimen source was blood.

CONCLUSION

In 2018, MenW was the most common serogroup for isolates received by the NML from culture-positive IMD cases in Canada. Over 90% of the MenW serogroup isolates belonged to the ST-11 CC. The quadrivalent ACWY meningococcal conjugate vaccine protects against IMD caused by strains in the A, C, W or Y serogroups and therefore may protect against IMD caused by the new MenW ST-11 strain; however, more research is needed. The emergence of variant strains highlight the importance of strain characterization in IMD surveillance and research.

Sandwich capture ELISA by a murine monoclonal antibody against a genus-specific LPS epitope for the detection of different common serotypes of salmonellas

A sandwich capture ELISA based on a murine monoclonal antibody against a genus-specific epitope in the outer core region of the Salmonella lipopolysaccharide is described for the detection of different common serotypes of salmonellas. Four h broth cultures of seven standard and 24 wild strains of salmonellas were all detected by the capture ELISA while overnight broth cultures of 21 non-salmonella standard strains were all negative. The capture ELISA detected 1 ng/ml of Ra lipopolysaccharide, 10(6)/ml of a smooth wild strain of Salm. typhimurium, and 1120 cells of Salm. heidelberg after enrichment culture for 4 h.

Detection of the lst gene in different serogroups and LOS immunotypes of Neisseria meningitidis

The sialylation of the lipooligosaccharide (LOS) of Neisseria meningitidis is mediated by the LOS sialyltransferase enzyme encoded by the lst gene. PCR using four sets of primers that targeted to different regions of the lst gene was used to survey the distribution of lst in different serogroups and LOS immunotypes of N. meningitidis as well as other Neisseria species. While the lst gene was found in N. meningitidis strains regardless of their capsular serogroup and LOS structures, the gene is also found in N. gonorrhoeae, N. lactamica, N. polysaccharea, and N. subflava biovar subflava. The presence of the lst gene in these organisms and the sialylation of their LOS antigens were discussed.

Flagella as a potential marker for Campylobacter jejuni strains associated with Guillain-Barré syndrome

Campylobacter jejuni recovered from patients with Guillain-Barré syndrome (GBS) in different geographical locations and bearing different heat-labile and heat-stable antigens were found to have identical amino acid sequences in their flagellar flaA short variable region, suggesting that it may be a potentially useful marker for GBS association.

Two murine monoclonal antibodies against serogroup E Salmonellae

A monoclonal antibody (MAb), MO15, was raised against the lipopolysaccharide antigen of an epsilon15-lysogenized serogroup E(1) Salmonella strain. The O factor 15-specific MAb MO15, together with another serogroup E-specific MAb, can differentiate among phage lysogenization variants in serogroup E salmonellae. Their epitope specificities in relation to conventional O-antigenic structures are discussed.

Screening for Salmonella with a murine monoclonal antibody M105 detects both Felix O1 bacteriophage sensitive and resistant Salmonella strains

Ten Felix O1 (FO1) bacteriophage sensitive Salmonella strains as well as their phage resistant derivates together with 39 strains of FO1-resistant Salmonella were tested for their reactivities with a murine monoclonal antibody, M105, by indirect whole cell and competitive ELISA. All FO1 phage sensitive and 48 of the 49 FO1-resistant Salmonella strains were found to react with M105. The single Salmonella strain not reacting with M105 was a FO1 resistant derivative selected by exposing the sensitive parent strain to the phage. This M105-negative and FO1-resistant strain was also found to be a rough mutant without O-antigens and possibly lacks the terminal LPS core sugars which form the M105 reactive epitope.

An enzyme-linked immunosorbent assay to detect PCR products of the rfbS gene from serogroup D salmonellae: a rapid screening prototype

We describe a digoxigenin-based enzyme-linked immunosorbent assay (DIG-ELISA) following a PCR to detect the amplified lipopolysaccharide rfbS gene as a means for rapid screening of serogroup D salmonellae in stool specimens. For pure bacterial cultures, the sensitivity of the PCR DIG-ELISA was approximately 10 bacteria. In the presence of stool materials, the salmonellae were first isolated by an immunomagnetic separation technique with an O9-specific monoclonal antibody. MATy-O9, followed by PCR and DIG-ELISA. The corresponding sensitivity was about 10 to 100 bacteria. To evaluate the assay performance clinically, 203 stool samples from patients with diarrhea were subjected to the routine culture techniques and the PCR ELISA method with overnight enrichment. The conventional culture method identified 145 salmonellae (31 serogroup B, 27 serogroup C, 83 serogroup D, and 5 serogroup E isolates) and 58 non-salmonella bacteria. The PCR ELISA method correctly identified all 82 serogroup D salmonellae (A405 by ELISA, 2.54 +/- 0.74) but was negative for the other Salmonella serogroups (A405, 0.26 +/- 0.08; n = 63) and non-Salmonella isolates (A405, 0.16 +/- 0.04; n = 58). In order to obtain a visible result, the assay takes approximately 6 h (PCR, 4 h; ELISA, 2 h), along with brief enrichment cultivation of the samples (from 4 to 16 h). Thus, the PCR DIG-ELISA offers a fast, accurate, semiquantitative means of detecting infectious agents such as salmonellae, and future robotic automation is possible.

Immunochemical characterization of a haemagglutinating antigen of Arcobacter spp

The Arcobacter haemagglutinin has been identified by Western immunoblot to be an immunogenic protein of about 20 kDa. The haemagglutinating activity is sensitive to proteolytic enzyme digestion and heat treatment of 80 degrees C and above. The Arcobacter haemagglutinin is possibly a lectin-like molecule binding to erythrocytes via a glycan receptor containing D-galactose as part of its structure.

Characterization and specificity controls of murine monoclonal antibodies against serogroup C1 Salmonella

Two IgG3 murine monoclonal antibodies, Cl-1 and Cl-2, that showed serologic specificities for the O antigens of serogroup C1 (0:6,7) Salmonella were established. The epitopes for the antibodies were found to reside on the repeating units of the serogroup C1 Salmonella lipopolysaccharide and were labile to sodium metaperiodate oxidation. Serologic reactivities of Cl-1 and Cl-2 were not inhibited by commercial monospecific antiserum to O antigen 7, but were inhibited to various degrees by anti-[O:6,7] serum. Both antibodies reacted strongly with all strains of serogroup C1 Salmonella that have either O:6(1),7, O:6(2),7, or O:6(1,2),7 antigens. Reactivities of Cl-1 and Cl-2 with the phage-14 lysogenized C1 strains that bear the phage-modified O antigen (O:6,7----O:6,7,14) were detected by slide agglutination method only and not by whole-cell enzyme-linked immunosorbent assay. Both Cl-1 and Cl-2 antibodies did not react with other O serogroups of salmonellae, nor with other Gram-negative or Gram-positive bacteria. The diagnostic value of these monoclonal antibodies together with a previously described monoclonal antibody against the serogroup C2 Salmonella was demonstrated using the slide agglutination method with monoclonal antibodies ascitic fluids.

Structural differences in the outer core region of lipopolysaccharides derived from members of the genus Salmonella

Spontaneous and P22-resistant rough mutants, respectively, selected from Salmonella IV (18: z36, z38:-) and S. djakarta (48: z4, z24:-), appeared to lack the epitope recognized by the T6 monoclonal antibody which had been previously shown to correspond to the terminal alpha-1,2-linked N-acetyl-D-glucosamine residue of the Salmonella lipopolysaccharide (LPS) Ra core. LPSs and core oligosaccharides were therefore prepared from these two rough mutants and analysed by chemical and serological methods. Sugar analyses as well as methylation and 13C-NMR studies indicated that rough mutants derived from these two serotypes indeed possessed outer core structures differing from those of the well-characterized Salmonella Ra core. Serological data corroborated the chemical findings. Proposed structures of the outer core regions of these two R-types are presented and the significance of the findings is discussed.

Epitope mapping of four monoclonal antibodies recognizing the hexose core domain of Salmonella lipopolysaccharide

Four murine monoclonal antibodies reactive with distinctive regions of the hexose core domain of Salmonella lipopolysaccharide (LPS) were generated and their epitope specificities were delineated. MAST 56 (IgG1) and MAST 50 (IgG3) antibodies elicited by immunizations with Salmonella typhimurium Rb1 and Rb2 mutants, reacted selectively in enzyme immunoassay with the LPS from rough mutants. In contrast, MATy 1 (IgM) and MATy 2 (IgG2b) antibodies raised by an attenuated Salmonella typhi 620 Ty strain were reactive with LPS from both smooth and rough Salmonellae. Immunoblotting analysis showed that MATy 1 distinguished only the bottom bands (naked LPS core) among the heterogeneous LPS populations, whereas MATy 2 gave a ladder pattern (reactive with both naked and O-chain-substituted LPS cores). Differential binding specificities of MATy 1 and MATy 2 antibodies to the naked and capped LPS cores were further analyzed utilizing S. typhimurium polysaccharide fractions with different O-chain:core ratios which were obtained after separation by Sephacryl S-200 chromatography. Steric effects on the antibody reactivity by the bulky O-polysaccharide chain were detected. The use of chemically defined native and synthetic saccharides as inhibitors, in combination with the conformation of the Salmonella core oligosaccharide, permitted the definition of antigenic determinants carried in the core domain recognized by each antibody: (i) the branches I and VIII are essential for MATy 1 recognition, (ii) the backbone III-IV-V for MATy 2, (iii) the backbone II-III-IV-V for MAST 56, and (iv) the backbone plus the branch III-IV-V-VIII for MAST 50. (formula; see text)

Characterization of murine monoclonal antibodies against serogroup B salmonellae and application as serotyping reagents

Six murine hybridoma monoclonal antibodies reactive with lipopolysaccharide antigens of Salmonella typhimurium were obtained from a fusion of immune spleen cells from mice immunized with S. typhimurium and NS1 myeloma cells. Four antibodies appeared to be specific for serogroup B salmonellae, while the remaining two antibodies were found to be cross-reactive with Salmonella paratyphi A. The exquisite specificities of the Salmonella serogroup B monoclonal antibodies were demonstrated by their unique reactivities with different serotypes of group B salmonellae but with neither other O serogroups of salmonellae nor a wide spectrum of standard strains of other bacterial species. Serotyping of salmonella strains by the slide agglutination method with two of the serogroup B-specific monoclonal antibodies demonstrated their usefulness as serotyping reagents for the identification of serogroup B salmonellae in a routine diagnostic bacteriology laboratory.

Lack of the alpha-1,2-linked N-acetyl-D-glucosamine epitope in the outer core structures of lipopolysaccharides from certain O serogroups and subspecies of Salmonella enterica

A total of 176 strains of Salmonella enterica representing 116 serotypes were tested for the presence of the T6 epitope of the alpha-1,2-linked N-acetyl-D-glucosamine residue by reaction with a murine monoclonal antibody T6 specific for this structure in the Salmonella Ra core lipopolysaccharide (LPS). All 20 serotypes (70 strains) belonging to serogroups A to E were positive for the T6 epitope while 29% of the 96 serotypes (106 strains) belonging to O serogroups F to 67 were negative; 12 serotypes (12 strains) of subspecies IIIb Salmonella were positive for the T6 epitope, but 10 serotypes (11 strains) of subspecies IIIa Salmonella were found to lack this epitope. In T6-positive strains, the epitope was accessible to antibody binding in both the unsubstituted free rough core LPS and in the rough core LPS substituted with a few repeating units of O side chains. The presence or absence of the T6 epitope in Salmonella strains was not affected by culture conditions, the source of the isolate, the age of the culture or the presence of fimbriae antigens.

Characterization and application of a murine monoclonal antibody that reacts specifically with the serogroup D1 Salmonella

A murine hybridoma cell line that produces monoclonal antibody (mAb) against the serogroup D1 Salmonella lipopolysaccharide (LPS) antigen was established. The trisaccharide tyvelose alpha 1----3 mannose alpha 1----4 rhamnose was shown to be involved in the reactive epitope of the mAb since this mAb reacted strongly with strains of serogroup D1 Salmonella but not with Salmonella strains from the O serogroups of A, B, and D2, and sodium meta-periodate was found to destroy the reactivity of the serogroup D1 O-antigen with the mAb. As such this mAb was found to be a useful serotyping reagent for the identification of serogroup D1 Salmonella, and for the differentiation of strains of serogroups D1 and D2 Salmonella which have identical flagellar H antigens.

A murine monoclonal antibody that recognizes a genus-specific epitope in the Salmonella lipopolysaccharide outer core

A murine monoclonal antibody 105 made from spleen cells of a mouse immunized with a mixture of common Salmonella serotypes reacted specifically with salmonellae from the most frequently encountered O serogroups of A (O:2) to E (O:3), and with strains from the less common O serogroups that represent the subspecies I, II, IIIb, IV, V and VI. Specificity for Salmonella was demonstrated by the lack of reactivity of monoclonal antibody 105 with any of the 30 other different species of Gram-positive and Gram-negative bacteria tested including 16 species in the family of Enterobacteriaceae. Studies to elucidate its binding epitope have shown that it reacts with the three distal sugar residues joined through specific anomeric linkages as present only in the Salmonella lipopolysaccharide outer core, which explains its specificity for the Salmonella. The failure of monoclonal antibody 105 to react with a subspecies IIIa Salmonella suggested a different outer core structure in this strain of Salmonella and also that monoclonal antibodies to the outer core of Salmonella lipopolysaccharide should be useful in the molecular analysis of their diversity.

Production and characterization of murine monoclonal antibodies specific for serogroups E1 and E4 Salmonella

Two anti-Salmonella serogroup E-specific monoclonal antibodies (MAbs) are described. Neither antibody reacted with any of the 58 strains of serogroups A-D Salmonella tested by enzyme immunoassays nor did they react with any of the 21 other species of enterobacteria, 15 species of other Gram-negative bacteria, and 6 species of Gram-positive bacteria. In contrast, all 14 strains of serogroups E1 and E4 Salmonella reacted with both antibodies. Ascitic fluids of these two antibodies agglutinated all 42 strains of serogroups E1 and E4 Salmonella tested by slide agglutination method but did not agglutinate any of the 107 strains of other serogroups of Salmonella. Lysogenic conversion of serogroup E1 Salmonella strains by phages epsilon 15 and epsilon 34 resulted in loss of reactivities of these strains with the MAbs.

Smooth lipopolysaccharide of Salmonella adelaide has an atypical Salmonella Ra core

Two wild isolates as well as two laboratory strains of Salmonella adelaide obtained from different geographical areas failed to react with a monoclonal antibody directed against the terminal alpha-1,2-linked N-acetylglucosamine residue of the outer core of Salmonella lipopolysaccharide (LPS). This finding was confirmed by the lack of reactivities of Salmonella Ra LPS with S. adelaide antiserum or of S. adelaide R oligosaccharide with Salmonella Ra serum. Furthermore, S. adelaide proved to be resistant to lysis by phage FO1, which binds to a receptor also believed to involve the terminal alpha-1,2-linked N-acetylglucosamine of the Salmonella R oligosaccharide. These results suggest that the outer core structure of S. adelaide LPS may be different from that of S. typhimurium and other Salmonella strains.

Release of Vi antigens from Salmonella typhi: implications for virulence and diagnosis

The release of Vi antigens from three clinical isolates of Salmonella typhi was measured by a Vi-specific monoclonal antibody. Large quantities of Vi antigens were detected in the culture supernates from all three strains using either passive latex agglutination or rocket immunoelectrophoresis. Vi antigens were also detected in broth cultures of S. typhi containing about 10(5) cells/ml using the sandwich enzyme linked immunosorbent assay. The significance of this finding in relationship to the virulence and the diagnosis of S. typhi was discussed.

Characterisation and application of a murine monoclonal antibody specific for the serogroup C2 Salmonella

An IgG3 murine monoclonal antibody (designated MO8) specific for the serogroup C2 Salmonella lipopolysaccharide (LPS) was generated by fusing mouse myeloma cells NS1 with spleen cells of BALB/c mice immunised with heat-killed S. manhattan. MO8 reacted with purified LPS prepared from serogroup C2 Salmonella but did not react with that prepared from other O serogroups, and its reactivity was also specifically absorbed by serogroup C2 Salmonella only. Polyacrylamide gel electrophoresis of the serogroup C2 LPS and subsequent immunoblotting with MO8 yielded multiple reactive bands giving a characteristic ladder pattern. The specificity of MO8 was further demonstrated in the slide agglutination test with 223 bacteria, of which only 25 belonging to serogroup C2 Salmonella reacted with the MO8 ascitic fluid. The specificity of MO8 makes it useful not only for the serological identification of Salmonella but also for the epitope analysis of the serogroup C2 LPS.

Murine monoclonal antibody specific for lipopolysaccharide of Salmonella serogroup A

To facilitate the routine identification of salmonellae and detailed studies of their lipopolysaccharides, we raised murine monoclonal antibodies against these organisms. We raised an immunoglobulin G1 antibody, MO2, which is specific for factor O2. By immunoblotting following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, MO2 was shown to bind only the lipopolysaccharide of Salmonella paratyphi A, giving a ladderlike reaction pattern with regularly spaced reactive bands. MO2 did not react against lipopolysaccharides of other Salmonella serogroups, including those of serogroups B, C, D, E, and L. Since the lipopolysaccharides of Salmonella serogroups A, B, D, and E are similar except for the presence of paratose in serogroup A organisms, this dideoxyhexose is therefore believed to be the immunodominant epitope for MO2. Consistent with the latter contention was the finding that periodate oxidation of the S. paratyphi A lipopolysaccharide did not destroy its antigenicity for MO2. In a slide agglutination test, MO2 was found to react specifically against all 12 clinical isolates of S. paratyphi A but not against 98 isolates of other salmonellae or 74 isolates of other bacteria and Candida albicans.

Production of Vi monoclonal antibodies and their application as diagnostic reagents

Serum antibodies to Vi antigen were detected in mice immunized with the purified antigen but not with Vi-bearing Salmonella typhi whole cells. Fusion of the spleen cells from one of the Vi antibody-producing mice with NSI myeloma cells produced four stable hybridomas that secreted antibodies to Vi. Monoclonal antibodies from these four clones were all of the immunoglobulin G class and, as determined by competition, appeared to have the same epitope specificity. Despite their immunoglobulin G nature, mouse ascitic fluids induced by one of the hybridomas strongly agglutinated the Vi-positive strains of S. typhi, S. dublin, and Citrobacter strain 5396/38. Thus, 10 clinical isolates of S. typhi but not 98 strains of other bacteria were reactive in slide agglutination tests with the monoclonal antibodies.

A murine monoclonal antibody specific for the outer core oligosaccharide of Salmonella lipopolysaccharide

Immunoglobulin G3 murine monoclonal antibody T6 specific for the lipopolysaccharide of Salmonella O serogroups A to E was established. By using R mutants of Salmonella spp., Escherichia coli, and Shigella spp., the major reactive epitope with T6 was tentatively identified as the terminal disaccharide, N-acetylglucosamine 1.2----alpha glucose, of the core oligosaccharide. T6 was reactive with 10 clinical isolates of each of the Salmonella O serogroups A to E but not with 58 isolates of other gram-negative bacteria. Its selective reactivity against Salmonella spp. renders T6 a potentially more useful reagent than the conventional polyvalent serum for the identification of Salmonella spp. It may also serve as a useful molecular tool for the study of the outer core structure of all Salmonella and related species.

Crossed immunoelectrophoretic analysis of anti-Salmonella typhi antibodies in sera of typhoid patients and carriers: demonstration of the presence of typhoid-specific antibodies to a non-O, non-H, non-Vi antigen

A veronal buffer extract of Salmonella typhi was used as the reference antigen and its corresponding rabbit antiserum as the reference antibody in crossed immunoelectrophoresis to analyze antibodies in sera obtained from typhoid patients and carriers. Four precipitating antibodies were regularly detected. Three were against antigens common to other gram-negative bacteria and one appeared to be typhoid specific. Of the three common antigens, one (antigen no. 7) formed a precipitin resembling in mobility and morphology the lipopolysaccharide antigen seen in crossed immunoelectrophoresis analysis of other gram-negative bacteria. The other (antigen no. 19) was heat labile and antigenically similar to the reported common antigen of Pseudomonas aeruginosa. The third (antigen no. 14), also heat labile, was present in members of the family Enterobacteriaceae but not the family Pseudomonas. The typhoid-specific precipitating antibody present in sera of most typhoid patients and carriers but not patients infected with nontyphoid salmonella was directed to a heat-labile, non-O, non-H, and non-Vi antigen (antigen no. 28), probably protein in nature.

Antigenic analysis of Barber's protein antigen prepared from Salmonella typhi and demonstration of protein-specific antibodies in sera of typhoid patients

A crude protein antigen (Barber's antigen) was prepared from Salmonella typhi by mild extraction with veronal buffer followed by repeated precipitation with trichloracetic acid according to the method of Barber. From serological studies and polyacrylamide gel electrophoresis, Barber's antigen was found to be highly heterogeneous and contain both the lipopolysaccharide and Vi antigens in addition to the protein antigens. Nevertheless antibodies specific to the proteins in the Barber's antigen were demonstrated in typhoid patients' sera by radioimmunoassay, indicating that proteins were also a major antigenic component of S. typhi and might play a role during typhoid infection.

Vi serology in screening of typhoid carriers: improved specificity by detection of Vi antibodies by counterimmunoelectrophoresis

A purified soluble Vi antigen was used in counterimmunoelectrophoresis (CIE), passive haemagglutination (HA) and solid phase radio-immunoassay (SPRIA) for detection of serum Vi antibody. Serum Vi antibody was detected in 13 of 14 chronic typhoid carriers by both CIE and HA. SPRIA studies showed that Vi antibodies in sera of these carriers were mainly of the IgG class. Successful treatment with amoxycillin in one carrier, who initially showed a positive Vi test, resulted in a reversion in 6 months to seronegativity as measured by Vi CIE. However, Vi antibody was also detected in 10 sera (3%) from 329 control subjects by HA but not by CIE. When the CIE assay was applied to 1030 serum specimens obtained from hospitalized patients, it was able to detect one typhoid carrier, but one (0.1%) non-carrier also gave a positive Vi CIE test. It is thus concluded that Vi CIE is more specific and no less sensitive than Vi HA for the detection of the typhoid carrier state. The finding by SPRIA that the anti-Vi antibodies present in typhoid carriers' sera were mainly of the IgG class further justified the use of CIE as a precipitation test for their detection.

Antibody response to the lipopolysaccharide and protein antigens of Salmonella typhi during typhoid infection. I. Measurement of serum antibodies by radioimmunoassay

Serum antibody responses to the lipopolysaccharide and protein antigens of S. typhi in typhoid patients were studied using a solid-phase radioimmunoassay technique. Sera from 24 adult typhoid patients and 20 non-typhoid adult controls were compared. As a group, sera from typhoid patients showed increased IgA, IgG and IgM immunoglobulin levels and gave significantly higher anti-LPS and anti-protein antibody titres in all three major immunoglobulin classes than did non-typhoid controls. Levels of antibodies against LPS or protein in sera of typhoid patients were highly variable with a skew distribution. A good correlation was found between antibody titres to the LPS antigen and those to a protein antigen. No correlation, however, was found between the anti-LPS antibody titres measured by radioimmunoassay and the anti-O antibody titres measured by the Widal agglutination test. Titration of anti-LPS or anti-protein antibodies by radioimmunoassay was found to be more sensitive and specific than Widal test for the serological diagnosis of typhoid fever. The advantages of measuring antibody response by radioimmunoassay over conventional Widal test are discussed.

Antibody response to the lipopolysaccharide and protein antigens of Salmonella typhi during typhoid infection. II. Measurement of intestinal antibodies by radioimmunoassay

Antibodies to the lipopolysaccharide (LPS) and protein antigens of S. typhi in secretions of small intestine obtained from 12 typhoid patients, four typhoid carriers and 16 non-typhoid control subjects were measured by a solid-phase radioimmunoassay technique. Intestinal secretions obtained from typhoid patients as a group had significantly higher anti-LPS and anti-protein antibodies than those from the control group. These antibodies were both IgM and IgA classes. There was no correlation between the IgM or IgA antibody levels in serum and those in the intestinal secretions. In the intestinal secretions obtained from typhoid carriers, on the other hand, only IgA-class antibodies to the LPS and protein antigens of S. typhi were present at high levels.

Serological diagnosis of typhoid fever by counterimmunoelectrophoresis

The sensitivity and specificity of counterimmunoelectrophoresis using three antigenic preparations obtained from Salmonella typhi were compared with those of the Widal test in the serological diagnosis of typhoid fever. A veronal buffer extract yielded precipitation lines against 50 (96%) out of 52 sera collected from patients with typhoid but against none out of 62 sera obtained from control subjects who did not have typhoid. Less satisfactory results were obtained by counterimmunoelectrophoresis when two other preparations, a protein extract (Barber antigen) and an ultrasonic lysate, were used as the antigens. By Widal test the rate of detection in patients' sera was 73% and the false-positive rate for control sera 16%. It is concluded that in an area where typhoid is endemic counterimmunoelectrophoresis using veronal buffer extract as the antigen is superior to the Widal test for serological diagnosis of typhoid fever. An additional advantage of counterimmunoelectrophoresis is that results may be obtained on the same day that the serum specimens are received.