Invasive Pneumococcal Disease (IPD) Laboratory Case Definition (LCD)

The Public Health Laboratory Network have developed a standard case definition for the diagnosis of diseases which are notifiable in Australia. This page contains the laboratory case definition for Invasive Pneumococcal Disease (IPD).

Page last updated: 25 February 2020

1 PHLN Summary Laboratory Definition

1.1 Condition:

Invasive Pneumococcal Disease (IPD).

1.1.1 Definitive Criteria

  • Isolation of Streptococcus pneumoniae from a normally sterile site;

    OR

  • Detection of nucleic acid of S. pneumoniae from a normally sterile site.

1.1.2 Suggestive Criteria

  • Detection of S. pneumoniae antigen from a normally sterile site (excluding urine);

    OR

  • Gram positive diplococci consistent with S. pneumoniae in CSF.

1.1.3 Special Considerations / Guide for Use

Not applicable.

2 Introduction

Streptococcus pneumoniae is commonly carried in the nasopharynx of healthy people, particularly in young children.

It is also an important pathogen which causes:

  • localised infection of the upper respiratory tract, such as otitis media and sinusitis;
  • disseminated infection most commonly manifest as primary bacteraemia, pneumonia and/or meningitis. Less common sites of infection include septic arthritis, osteomyelitis, empyema, peritonitis and endophthalmitis.

Otitis media, of which S. pneumoniae is considered the commonest bacterial cause, is associated with significant morbidity in young children, including permanent hearing loss. However, in most cases the cause is rarely confirmed due to difficulty in acquiring a suitable specimen for culture. Similarly, pneumococcal pneumonia causes significant morbidity and mortality, predominantly in the elderly and immunocompromised, with a specific bacterial diagnosis confirmed in the minority in whom there is an associated bacteraemia and/or empyema. In addition, Gram stain and culture of respiratory tract specimens, such as sputum, conjunctiva and sinuses, cannot not reliably differentiate infection from colonising normal flora.

Due to these diagnostic problems, epidemiological studies generally define invasive pneumococcal disease (IPD) as isolation of S. pneumoniae by culture and/or detection of nucleic acid of S. pneumoniae from normally sterile sites. This results in underrepresentation of the total disease burden, however, the data still provides an objective measure of severe disease and is essential for continued surveillance to monitor vaccine efficacy.

The annual incidence of IPD in Australia has most recently ranged from 6.3-8.4/100,000, with variation seen among jurisdictions (ACT 5.1/100,000 and Northern Territory 22.2/100,000 (2018)). The incidence is significantly higher at the extremes of age - children under five and adults 70 years and over (19.4 and 15.2-41.3/100,000 (2018) respectively).1,2 IPD is also significantly more common in indigenous Australians (34-58.6/100,000 (2006-2015)), accounting for 16% of cases of IPD in 2015 where the indigenous status was known.1,2

In children, primary bacteraemia is the commonest manifestation of IPD (70%), followed by pneumonia with bacteraemia and meningitis. Most adults with IPD have pneumonia with bacteraemia.3

The major virulence factor of S. pneumoniae is its polysaccharide capsule which protects it from phagocytosis and is the basis for serotyping. There are about 90 pneumococcal serotypes. Most disease is caused by a limited number of serotypes, the distribution of which varies across different geographic areas, with different disease manifestations and in different age groups. Host antibodies, either from natural exposure or immunisation, are directed against the capsular polysaccharides.

As of 2019, the 23-valent polysaccharide pneumococcal vaccine (introduced in 1999 for indigenous and in 2005 for non-indigenous adults) is currently recommended for all adults 65 years and over, all Aboriginal and Torres Strait Islander 50 years and over, and all adults with medical conditions which put them at increased risk of IPD.3

After introduction of the 7-valent conjugate pneumococcal vaccine (7vPCV) for infants in Australia in 2005, the notification rate of IPD due to 7vPCV serotypes decreased in all age groups.4,5 However, rates of IPD caused by serotypes that were not contained in 7vPCV increased in Australia and several other countries.6 It was particularly evident among non-Indigenous children aged <5 years, where infections due to non-vaccine serotypes increased by 168%. The current 13-valent conjugate pneumococcal vaccine (introduced in 2012) is recommended in Australia for all infants. By 2014, there was a 42% reduction in IPD due to 13vPCV-non-7vPCV serotypes (reduced to 1.8 per 100,000). Serotype 19A caused around 80% of 13vPCV-type disease in children and around 40% in adults before 13vPCV was introduced. Introducing 13vPCV reduced disease caused by serotype 19A by almost 70% overall.5

Systematic surveillance of IPD is important to continue to monitor changes in the incidence and serotype distribution following introduction of vaccines and antibiotic resistance of isolates. IPD is a notifiable disease in Australia.

3 Tests

3.1 Gram Stain and Culture

3.1.1 Methods

S. pneumoniae may be detected by Gram stain of specimens or centrifuged fluids. It typically appears as Gram positive, lancet shaped diplococci or cocci in chains. These features may be altered by antimicrobial treatment and over decolourisation, giving the appearance of Gram negative diplococci.

Blood is inoculated into highly nutrient, commercial blood culture media. Blood culture bottles with evidence of bacterial growth, and other specimens (sterile site and respiratory) are typically plated on blood agar with an optochin disc and incubated aerobically and in 5% CO2, and on chocolate agar incubated in 5% CO2. Following overnight incubation S. pneumoniae appears as optochin sensitive, small, greyish mucoid (i.e. capsule-producing) colonies with alpha-haemolysis. Typically, over the next 24-48 hours the colonies develop a central depression or “draughtsmen-like” shape.

S. pneumoniae is differentiated from other viridans-type streptococci by their susceptibility to optochin (ethylhydrocupreine) and, if necessary, bile solubility (autolysis in the presence of sodium deoxycholate).

Commercial biochemical identification systems are generally not necessary and may have difficulty in differentiating S. pneumoniae from other viridans-type streptococci.

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has the advantage over traditional phenotypic identification methods by providing more rapid identification. However, due to specificity concerns associated with misidentification of S. mitis species group as S. pneumoniae, MADLI-TOF MS identification is usually supplemented by optochin susceptibility.

3.1.2 Quality Assurance

3.1.2.1 Suitable specimens

Any sterile site specimen where infection with S. pneumoniae is suspected is suitable for Gram stain and culture. Sensitivity of culture is maximised when specimens are taken prior to antibiotics, however, this is not always clinically possible, particularly in the case of suspected bacterial meningitis. Centrifugation of fluid specimens is recommended to improve sensitivity for Gram stain and culture.

3.1.2.2 Test sensitivity

Pneumococcal meningitis is usually associated with CSF findings typical of bacterial meningitis - a predominant polymorphonuclear pleocytosis, high protein and low glucose levels. However, in fulminating cases there may be relatively few (occasionally no) polymorphonuclear cells but large numbers of bacteria, which can cause obvious turbidity, even in the absence of cells. The bacteria are usually obvious in the counting chamber (but can be overlooked), and their presence is confirmed by Gram stain of the centrifuged deposit.

CSF Gram stain has a sensitivity of 84% in detecting S. pneumoniae, however this is significantly reduced with prior administration of antibiotics.8

Sensitivity of culture depends on the clinical setting, volume of specimen cultured and whether or not antibiotics have been given prior to specimen collection. Processing a CSF specimen, as well as other clinical specimens, for culture as soon as possible is vital for optimal culture performance, because bacterial viability decreases over time. Blood cultures become negative soon after antibiotic therapy is started.

About 3-10% of untreated patients with pneumococcal pneumonia and >50% of those with meningitis have positive blood cultures.7,9,10

Resistance to optochin is reported among 10% of S. pneumoniae isolates. In circumstances of optochin resistance, where S. pneumoniae is highly suspected due to clinical and/or other laboratory features (i.e. Gram stain appearance and/or colony morphology), further testing is required for identification and differentiation from other viridans-type streptococci. Bile solubility is highly sensitive and specific for S. pneumoniae.

The sensitivity of MALDI-TOF MS is high (92-100%).11,12 The Vitek Compact system (bioMérieux) has slightly lower sensitivity (88.5%) associated with misidentification of S. pneumoniae as other viridans-type streptococci.12

3.1.2.3 Test specificity

The typical Gram stain appearance of S. pneumoniae in sterile site specimens has high specificity when observed by an experienced microscopist. The specificity for meningitis is 98%.8 Accurate results are highly dependent on the operator’s staining and interpretation skills.

Isolation of S. pneumoniae by culture from blood or other normally sterile specimens has 100% specificity for IPD. However, care must be taken not to mistake Streptococcus pseudopneumoniae for S. pneumoniae on the basis of optochin susceptibility when incubated in ambient air and/or following streptococcal antigen positivity. S. pseudopneumoniae has intermediate susceptibility or resistance to optochin when incubated in 5% CO2, is insoluble in bile and lacks a capsule.14,15 The Vitek MS (bioMérieux) system has been shown to differentiate S. pneumoniae from S. pseudopneumoniae.9

Non-pneumococcal viridans-type streptococci, especially S. mitis and S. oralis, may be misidentified as S. pneumoniae by MALDI-TOF MS, however the specificity of commercial systems appears to be improving. The Vitek MS (bioMérieux) system has demonstrated a specificity of 100%.11,12 The specificity of the MALDI-TOF Biotyper (Bruker Daltonics) system for S. pneumoniae identification was 92.4% (10 non pneumococcal isolates were misidentified as S. pneumoniae) after the January 2014 upgrade of the database, but only 49% with the precedent version (67 non pneumococcal isolates were misidentified as S. pneumoniae).12,16 In the same analysis, the specificity of the VITEK Compact system (bioMérieux) for S. pneumoniae identification was 100%.12

3.1.2.4 Predictive values

For most populations, the positive predictive value of a positive culture from blood or sterile sites is near 100% due to the high specificity of culture.

The negative predictive value depends on the pre-test probability of IPD which is most influenced by risk factors (particularly age, indigenous status and co-morbidities such as human immunodeficiency virus, asplenia and hypogammaglobulinaemia), clinical features, supporting radiology and pathology testing (i.e. CSF microscopy, protein and glucose) and prior antibiotics (as reduces sensitivity). Failure to isolate S. pneumoniae from blood of a patient with apparently typical pneumococcal pneumonia is common. Negative CSF culture does not exclude the diagnosis of pneumococcal meningitis.

3.1.2.5 Suitable acceptance criteria

Isolation of a S. pneumoniae: typical Gram positive diplococci or cocci in chains growing as alpha haemolytic colonies on blood agar confirmed by optochin susceptibility +/- bile solubility.

3.1.2.6 Suitable internal controls

All media and tests should have properly documented, relevant quality control using ATCC or NCTC control strains.

3.1.2.7 Suitable test validation criteria

All tests performed need to be validated as per NPAAC criteria before reporting for clinical management purposes.

3.1.2.8 Suitable external QA program

Participation in a suitable external QA program, such as Royal College of Pathologist of Australasia Quality Assurance Program Pty. Ltd. (RCPA).

3.2 Nucleic Acid Amplification Tests (NAATs)

3.2.1 Methods

A number of in-house or commercial NAATs, mainly polymerase chain reaction (PCR), have been described to detect the presence of S. pneumoniae DNA. They include multiplex PCR for simultaneous detection of common causes of bacterial meningitis. The pneumolysin gene (ply), autolysin gene (lytA), pneumococcal surface adhesin A gene (psaA), wzg/cpsA, and the Spn9802 gene fragment have been used as PCR targets to detect S. pneumoniae.10

3.2.2 Quality Assurance

3.2.2.1 Suitable specimens

Clinical specimens used to detect invasive S. pneumoniae have included whole blood or serum,17-19 CSF20 and transthoracic needle aspirates.21 However all specimen types may not necessarily be verified/validated against NPAAC standards for the detection of S. pneumoniae DNA, with their role in routine diagnosis across various specimens yet to be defined.

3.2.2.2 Test sensitivity

Nucleic acid amplification tests do not require viable bacteria for a positive result and are generally considered highly sensitive. PCR inhibitors in clinical specimens can compromise sensitivity. In the setting of pneumonia, NAATs have a sensitivity for detecting S. pneumoniae in blood samples ranging from 29% to 100%, although there is a tendency for the performance to be better in children than in adults.7,10 NAATs using the autolysin gene (lytA) have been shown to have greater sensitivity over pneumolysin gene (ply).9,10

The sensitivity of NAATs applied to CSF samples for diagnosis of pneumococcal meningitis is 92%–100%.7

NAATs have also been successfully used with other samples obtained by invasive means, such as pleural fluid and lung aspirate specimens.7,9

3.2.2.3 Test specificity

As with all NAATs, care must be taken to prevent contamination. Pneumolysin gene (ply) can be detected in non-pneumococcal viridans-group streptococci, particularly S. pseudopneumoniae and S. mitis, which is thought to have contributed to positive pneumococcal NAAT results from blood in asymptomatic control subjects and poor performance in the detection of pneumococcal disease.7,9,10 Other targets, including the autolysin gene (lytA), the pneumococcal surface adhesion gene (psaA), and the spn9802 gene fragment, appear to be more specific.9

The specificity of pneumococcal NAAT applied to CSF samples is reported at 100%.7

3.2.2.4 Predictive Values

The positive predictive and negative predictive values are influenced by the sensitivity and specificity of the test, and vary according to the pre-test probability of IPD. Results should always be correlated with the clinical features and results of other diagnostic tests.

3.2.2.5 Suitable acceptance criteria

General acceptance criteria for nucleic acid detection include:

  • Absence of detectable contamination.
  • Successful detection of positive control material.
  • Absence of inhibition in the clinical material.
3.2.2.6 Suitable internal controls

Positive and negative control material should be included in the extraction stage and all subsequent amplification steps.

3.2.2.7 Suitable test validation criteria

Positive and negative control material should be included in the extraction stage and all subsequent amplification steps.

3.2.2.8 Suitable external QA program

Participation in a suitable external QA program.

3.3 Antigen Detection

3.3.1 Methods

There are two targets for antigen detection – the capsular polysaccharide and cell wall teichoic acid (C polysaccharide).

Capsular polysaccharide was first detected in the urine of patients with pneumococcal pneumonia in 1917, however levels in the urine of these patients were variable and dependent on the serotype. The latex agglutination test to detect urinary capsular polysaccharide of S. pneumoniae, was of limited usefulness because of limited sensitivity and specificity.9,10

C polysaccharide cell wall antigen is common to all strains of S. pneumoniae and is detected using a rapid immunochromatographic test (ICT) (Binax NOW S. pneumoniae urinary antigen test).7

3.3.2 Suitable specimens

While primarily designed and marketed as a urinary antigen test, studies have also shown the utility of the C polysaccharide antigen ICT in the identification of S. pneumoniae from CSF, pleural fluid, bronchoalveolar lavage (BAL), and blood culture media in both adult and pediatric patients. The use of antigen detection from sterile sites may be a better alternative than urine detection, especially in children.9

3.3.3 Test sensitivity

The C polysaccharide antigen ICT (Binax NOW) has reported sensitivity in urine for pneumonia in adults of 70-92% (higher for bacteraemic vs non-bacteraemic pneumonia), in pleural fluid for pneumococcal empyema of 71-96% and in CSF for meningitis of 95-100%.7,10

One advantage of the C polysaccharide antigen ICT (Binax NOW) is that prior antibiotic use has less influence on the diagnostic yield.10

3.3.4 Test specificity

In adults, the specificity of the C polysaccharide antigen ICT (Binax NOW) in urine for the diagnosis of community acquired pneumonia is 67-100%.9 However, studies of urine samples from children have showed inadequate specificity (50-60%) due to the high rate of nasopharyngeal carriage in children, resulting in urinary excretion of teichoic acid.10 False positives also occur following pneumococcal vaccination, due to cross reaction with other closely related streptococci (including S. pseudopneumoniae) or following resolved infection, as the test may remain positive several weeks after infection.7,9 In addition, a positive urinary antigen test cannot distinguish pneumonia without invasive disease from IPD.

The specificity for other fluids is high, including 100% for CSF, 71-100% for pleural fluid and 87% for BAL.7,10

3.3.5 Predictive Values

The positive predictive and negative predictive values are influenced by the sensitivity and specificity of the test for the specimen type, and vary according to the pre-test probability of IPD. A positive C polysaccharide antigen ICT (Binax NOW) from CSF with elevated polymorphonuclear cells has very high positive predictive value. Results should always be correlated with the clinical features and results of other diagnostic tests.

3.3.6 Suitable acceptance criteria

Presence of control line for each test using the C polysaccharide antigen ICT (Binax NOW).

3.3.7 Suitable internal controls

Positive and negative controls supplied in the kit; or human urine containing S. pneumoniae antigen (positive control) and normal human urine (negative control).

3.3.8 Suitable test validation criteria

Positive and negative controls supplied in the kit; or human urine containing S. pneumoniae antigen (positive control) and normal human urine (negative control).

3.3.9 Suitable external QA program

Participation in a suitable external QA program, such as Royal College of Pathologist of Australasia Quality Assurance Program Pty. Ltd. (RCPA).

3.4 Antibody Detection

Use of antibody tests for the routine diagnosis of acute S. pneumoniae infection is not recommended due to suboptimal sensitivity and specificity, and time taken to demonstrate seroconversion. In addition, antibody detection is unable to differentiate IPD from non-invasive pneumococcal disease.

4 Agreed Typing & Subtyping Methods

S. pneumoniae is divided into at least 90 serotypes, based on differences in capsular polysaccharide antigens. The Quellung reaction is the gold standard method for pneumococcal capsular serotyping. The method involves testing a pneumococcal cell suspension with pooled and specific antisera directed against the capsular polysaccharide. Serotyping is not required for individual patient management but may sometimes be useful for investigation of case clusters and recurrent invasive disease. However, with the widespread use of conjugate vaccines, routine surveillance of isolates from all cases of invasive pneumococcal disease, and potentially selected clinically significant isolates from respiratory sites, will be required to monitor changes in serotype distribution.

In 2015 serotypes 19A, 3, 22F, 19F, 9N and 7F caused 43% of IPD. All but 22F and 9N are included in the 13-valent pneumococcal conjugate vaccine. The remainder of cases were due to 36 different serotypes.1

The serotypes are grouped on the basis of antigenic similarities. On exposure of pure culture to specific anticapsular antiserum, the capsule becomes enhanced and bacterial cell appears surrounded by a halo, as observed under the light microscope. Standard antiserum pools are available for the main serogroups and individual serotypes (Table 1). As of 2019, serotyping is currently performed in four Australian laboratories (Microbiological Diagnostic Unit, Victoria; Institute of Clinical Pathology and Medical Research (ICPMR)-NSW Health Pathology, New South Wales; Queensland Forensics and Scientific Services, Queensland; and PathWest Laboratory Medicine WA, Queen Elizabeth II Medical Centre, Western Australia).

As up to 10% of IPD is diagnosed on the basis of nucleic acid detection in the absence of culture. Direct molecular typing is also available (Microbiological Diagnostic Unit, Victoria; Institute of Clinical Pathology and Medical Research (ICPMR)-NSW Health Pathology; Queensland Forensics and Scientific Services). The molecular typing currently covers all serotypes in the conjugate 13-valent vaccine and some additional types, however is not always able to distinguish a single factor type, therefore multiple results may be given (e.g. 15B/C, 11A/D/18F, 47F/35F). In a significant number of cases where molecular typing is attempted, a serotype is unable to be determined, mainly due to the insufficient amounts of S. pneumoniae DNA present in those samples.

Table 1: List of serotypes

1
9V
15B
23F
35A
2
10F
15C
23A
35B
3
10A
16F
23B
35C
4
10B
16A
24* (24F, 24A, 24B)
36
5
10C
17F
25* (25F,25A)
37
6A
11F
17A 18F
27
38
6B
11A
18A
28* (28F,28A)
39
6C
11B
18B
29
40
6D
11C
18C
31
41* (41F, 41A)
7F
11D
19F
32*(32F,32A)
42
7A
12F
19A
33F
43
7B
12A
19B
33A
44
7C
12B
19C
33B
45
8
13
20
33C
46
9A
14
21
33D
47
9L
15F
22F
34
48
9N
15A
22A
35F

* Grouping sera only are kept in Australia for these rare serogroups.

5 Antimicrobial Susceptibility

Changes in S. pneumoniae antimicrobial susceptibility evolved rapidly internationally from the 1990s, with penicillin non-susceptibility (intermediate and resistant) of particular concern. Susceptibility has varied according to geographical location, site of infection and pneumococcal serotype. Australian data from 2007 demonstrated stabilisation or reduction in non-susceptibility rates (following alarming increases around the late 1990s/early 2000s) for parenteral penicillin (25% using meningitis breakpoints and <5% using non-meningitis breakpoints), erythromycin (20.4%), clindamycin (15.4%), tetracycline (17.7%) and trimethoprim-sulphamethoxazole (28%).22 Moxifloxacin non-susceptibility was rare (0.3%).22 Non-susceptibility rates were higher for non-invasive isolates compared to invasive isolates.

Three main standards for reporting antimicrobial susceptibility are used in Australian laboratories – European Committee on Antimicrobial Susceptibility Testing (EUCAST),23 Clinical and Laboratory Standards Institute (CLSI)24 and Calibrated Dichotomous Susceptibility (CDS).25 Reporting and interpretation of penicillin susceptibility for S. pneumoniae is complicated by different breakpoints for non-meningitis vs meningitis isolates and oral vs parenteral agents, and variable dosing recommendations based on the minimum inhibitory concentration (MIC). From 2019, EUCAST has recommended that “Intermediate” breakpoints (traditionally regarded as non-susceptible) are reported and interpreted as “Susceptible – Increased Exposure”, recognising that favourable clinical outcomes may be achieved when adequate drug concentrations are maintained at the site of infection. CLSI continues with an “Intermediate” classification, to also account for variability in laboratory performance, whilst CDS uses the terminology “Decreased Susceptibility”. Tables 2-4 compare the breakpoints of the three methods for the antibiotics commonly used.

Resistance to beta lactam antibiotics (such as penicillin) is associated with changes to one or more of the penicillin binding proteins (PBP 1A, 1B, 2A, 2b and 2X). There are currently no genotypic resistance assays for beta-lactam or other classes of antibiotics used routinely in clinical laboratories.

Table 2: Beta-lactam antibiotic susceptibility interpretations for S.pneumoniae based on MIC (mg/L) breakpoints* according to EUCAST23 and CLSI24 standards (July 2019)

Antibiotic
Susceptible (S)
Intermediate (CLSI)
Susceptible Increased Exposure (EUCAST)
Resistant (R)
EUCAST
CLSI
EUCAST
CLSI
EUCAST
CLSI
Benzylpenicillin
(non-meningitis)
≤0.06
≤2
0.12-2
4
>2
≥8
Benzylpenicillin
(meningitis)
≤0.06
≤0.06
-
-
>0.06
≥0.12
Phenoxymethylpenicillin
Oxacillin 1ug disc >=20mm
≤0.06
-
0.12-1
Oxacillin 1ug disc <20mm
≥2
Amoxicillin/ampicillin
(intravenous)
≤0.5
-
1-2
-
>2
-
Amoxicillin
(non-meningitis)
-
≤2
-
4
-
≥8
Amoxicillin (oral)
≤0.5
-
1
-
>1
-
Ceftriaxone/cefotaxime
(non-meningitis)
≤0.5
≤1
1-2
2
>2
≥4
Ceftriaxone/cefotaxime
(meningitis)
≤0.5
≤0.5
1-2
1
>2
≥2

*NOTE: medium, inoculum and incubation requirements may vary between the two methodologies.
Breakpoints for disc diffusion also available for some antibiotics.

Table 3: Antibiotic susceptibility interpretations for S.pneumoniae according to CDS25 standards (July 2019)

Antibiotic Susceptible (S) Decreased Susceptibility Resistant (R)
Benzylpenicillin
(non-meningitis)
0.5u disc
≥6mm
0.5u disc <6mm AND
Ampicillin 5ug disc ≥4mm
0.5u disc <6mm AND
Ampicillin 5ug disc <4mm
Benzylpenicillin
(meningitis)
-
0.5u disc
< 6mm
Amoxicillin/ampicillin (non-meningitis)
5ug disc
≥4mm
5ug disc ≥4mm-AND
0.5u benzylpenicillin disc <6mm
5ug disc
< 4mm
Ceftriaxone/cefotaxime
(non-meningitis)
0.5ug disc
≥4mm
0.5ug disc <4mm AND
5ug disc ≥4mm
5ug disc <4mm
Ceftriaxone/cefotaxime
(meningitis)
-
0.5ug disc
< 4mm


Table 4: Antibiotic susceptibility interpretations for S.pneumoniae based on MIC (mg/L) breakpoints* according to EUCAST23 and CLSI24 standards, and CDS25 standards (July 2019)

Antimicrobial CDS
Disc Strength
Angular radius
S ≥6mm
R <6mm
Susceptible (S) Intermediate (CLSI)
Susceptible Increased Exposure (EUCAST)
Resistant (R)
EUCAST CLSI EUCAST CLSI EUCAST CLSI
Erythromycin
5ug
≤0.25
≤0.25
0.5
0.5
>0.5
≥1
Clindamycin#
2ug
≤0.5
≤0.25
-
0.5
>0.5
≥1
Tetracycline^
10ug
≤1
≤1
2
2
>2
≥4
Moxifloxacin
2.5ug
≤0.5
≤1
-
2
>0.5
≥4
Trimethoprim-sulphamethoxazole
1.25/23.75ug
≤1
≤0.5
2
1-2
>2
≥4

*NOTE: medium, inoculum and incubation requirements may vary between the two methodologies. Breakpoints for disc diffusion also available for some antibiotics.
# If inducible resistance then report as resistant
^ Organisms susceptible to tetracycline are susceptible to doxycycline however doxycycline resistance cannot be inferred from tetracycline

6 Laboratory Nomenclature for National Database Dictionary

6.1 Organism Name(s) List

SNOMED CT concept Code
Invasive pneumococcal disease (disorder)
406617004
Pneumococcal infectious disease
16814004
Streptococcus pneumoniae (organism)
9861002
Multiple drug-resistant Streptococcus pneumoniae (organism)
409806004
Streptococcus pneumoniae serotype 3 (organism)
103497003
Streptococcus pneumoniae serotype 19A (organism)*
415611002
Streptococcus pneumoniae DNA (substance)
708447006
Streptococcus pneumoniae antigen (substance)
120985002
Streptococcus pneumoniae pneumonia (finding)
717216007
Streptococcus pneumoniae antigen assay (procedure)
122120003
Bacterial serotyping (procedure)
57906000

*specific codes for other serotypes can be accessed from SNOMED-CT browsers

7 References

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