Aura 2016: first Australian report on antimicrobial use and resistance in human health

4.12 Streptococcus agalactiae

Health impact

S. agalactiae, also called group B Streptococcus (GBS), occasionally causes infections similar to those caused by S. pyogenes. These include skin and soft tissue infections, as well as more serious infections, such as septicaemia and bone and joint infections. Its greatest significance is as the main cause of neonatal septicaemia and meningitis, which is associated with high morbidity and mortality. The neonate acquires the organism from the mother’s vaginal flora, where it is carried asymptomatically. The organism is carried by up to 30% of healthy women of childbearing age.

Treatment

Screening mothers in late pregnancy for carriage of GBS is now widespread practice in Australia. If the mother tests positive for GBS, antimicrobials are administered to her during delivery to prevent transmission to the baby, regardless of the delivery mode. Benzylpenicillin is the recommended agent for this purpose; cefazolin or lincomycin/clindamycin are recommended for women with penicillin allergy, depending on the type and severity of the allergy.

Types and impact of resistance

Resistance to benzylpenicillin and cefazolin is emerging but still uncommon in Australia, but resistance to erythromycin/lincomycin/clindamycin is common at around 20%. Lincomycin/clindamycin resistance is strongly linked to resistance to macrolides such as erythromycin, which is often used in the laboratory as the test agent to predict resistance to lincomycin/clindamycin. Mothers who carry GBS that is resistant to erythromycin/lincomycin/clindamycin, but who would otherwise be treated with lincomycin/clindamycin, will require prophylaxis with vancomycin.

Key findings (Queensland)

Resistance to (benzyl)penicillin was not found, but resistance to erythromycin exceeded 20% (Figure 4.37). This is important, because an erythromycin resistance rate of 20% is the threshold at which protocols may need to be reconsidered and alternative agents used.

Resistance to (benzyl)penicillin was not found in S. agalactiae, but resistance to erythromycin exceeded 20%.

Figure 4.37 Streptococcus agalactiae resistance to individual agents, 2014

Sources: OrgTRx (Queensland); Sullivan Nicolaides Pathology (Queensland and northern New South Wales)

4.13 Streptococcus pneumoniae

Health impact

S. pneumoniae is an important pathogen that commonly causes acute otitis media, acute sinusitis and pneumonia. It can also cause septicaemia (especially in young children) and bacterial meningitis. Its capacity to cause disease is linked to its polysaccharide capsule, of which there are more than 90 serotypes.

In Australia, two pneumococcal vaccines are included in the National Immunisation Program. Infants receive a conjugated vaccine that covers 13 of the most common serotypes, and older people and those with risk factors receive a polysaccharide vaccine that covers 23 of the most common serotypes. Hence, not all pneumococcal infection is preventable.

Treatment

Otitis media and sinusitis are normally treated with oral amoxicillin, cefuroxime (in penicillin-allergic patients) or doxycycline (for people older than eight years). Macrolides and trimethoprim–sulfamethoxazole are sometimes used for oral treatments. Pneumonia and meningitis are generally treated with benzylpenicillin if the strain is proven to be susceptible, or ceftriaxone (or cefotaxime) for penicillin-nonsusceptible strains. Strains causing pneumonia or meningitis that are nonsusceptible to penicillin and ceftriaxone (rare) require treatment with vancomycin or meropenem, or sometimes both.

Types and impact of resistance

Reduced susceptibility to benzylpenicillin emerged in S. pneumoniae some decades ago and has continued to increase. This resistance can mostly be managed with increased dosing regimens of benzylpenicillin, or amoxicillin when oral treatment is appropriate. However, strains with reduced susceptibility causing meningitis are resistant to treatment with benzylpenicillin due to the relatively poor penetration of this antimicrobial into the subarachnoid space (where the infection is located). Meningitis caused by these strains requires treatment with ceftriaxone (or cefotaxime), unless the strains also have reduced susceptibility to these agents.

Resistance to tetracycline predicts resistance to doxycycline, and is a feature of multidrug-resistant strains.

Key findings (Queensland)

Resistance to (benzyl)penicillin was low, but rates of resistance to macrolides (erythromycin), tetracycline and trimethoprim–sulfamethoxazole were all above 20% (Figure 4.38). Rates of resistance were somewhat lower for blood isolates than isolates from other specimens. There were no major differences in resistance rates in different clinical settings (Figure 4.39).

Resistance to (benzyl)penicillin was low, but rates of resistance to erythromycin, tetracycline and trimethoprim–sulfamethoxazole were all above 20%.

Figure 4.38 Streptococcus pneumoniae resistance to individual agents used in treatment, 2014

ERY = erythromycin; PEN = benzylpenicillin; SXT = trimethoprim–sulfamethoxazole; TET = tetracycline

Note: Benzylpenicillin resistance is defined as a minimum inhibitory concentration of >2 mg/L (infections other than meningitis) (European Committee on Antimicrobial Susceptibility Testing).

Sources: OrgTRx (Queensland); Sullivan Nicolaides Pathology (Queensland and northern New South Wales)

Data table: Figure 4.38

Agent	Blood (n = 175), % resistant	Other (n = 2,291), % resistant
PEN	2.3	2.0
ERY	21.1	25.9
TET	21.1	25.6
SXT	21.1	29.9

Figure 4.39 Streptococcus pneumoniae resistance, by clinical setting, 2014

ERY = erythromycin; na = not available (either not tested or tested against an inadequate number of isolates); PEN = benzylpenicillin; SXT = trimethoprim–sulfamethoxazole; TET = tetracycline

Note: Benzylpenicillin resistance is defined as a minimum inhibitory concentration of >2 mg/L (infections other than meningitis) (European Committee on Antimicrobial Susceptibility Testing).

Sources: OrgTRx (public hospitals and health services); Sullivan Nicolaides Pathology (private hospitals and community)

Data table: Figure 4.39

Agent	Public hospitals and health services (n = 1,333), % resistant	Private hospitals (n = 131), % resistant	Community (n = 1,001), % resistant
Penicillin	2.6	3.1	1.3
Erythromycin	22.1	30.0	29.6
Tetracycline	na	26.6	0.0
Trimethoprim-sulfamethoxazole	na	27.5	30.0