Streptococcus spp.

Associated infections

• Pharyngitis and tonsillitis
• Scarlet fever
• Impetigo, cellulitis and erysipelas
• Necrotising fasciitis
• Streptococcal toxic shock syndrome
• Community-acquired pneumonia
• Otitis media and sinusitis
• Bacterial meningitis
• Bacteraemia and sepsis
• Infective endocarditis
• Neonatal sepsis and early-onset neonatal disease
• Puerperal sepsis and postpartum infection
• Septic arthritis and osteomyelitis
• Post-streptococcal acute rheumatic fever and glomerulonephritis

Transmission route

Streptococci spread principally by person-to-person routes. Streptococcus pyogenes and Streptococcus pneumoniae are transmitted by respiratory droplets and by direct contact with respiratory secretions, and S. pyogenes additionally by contact with skin lesions and, historically, by contaminated food. Streptococcus agalactiae is transmitted vertically from a colonised maternal genital tract to the infant during labour and delivery. Asymptomatic carriage precedes and sustains all of these routes: a substantial proportion of healthy adults and a higher proportion of children carry S. pneumoniae in the nasopharynx at any time, and carriage of S. pyogenes in the throat is common in school-age populations.

Invasive disease more often arises endogenously, when an organism already colonising a mucosal surface breaches the epithelium, than from an exogenous environmental source. Preceding viral infection, mucosal injury, skin breaks, surgery and instrumentation all facilitate this. In healthcare settings, outbreaks of invasive group A streptococcal disease have been traced to colonised staff members and to breaches in aseptic technique in obstetric and surgical care, which is a reminder that the transmission route of concern is human rather than environmental.

The genus has no environmental reservoir in treated water and no recognised capacity to establish or persist within purified-water distribution systems, reverse-osmosis membranes or automated endoscope reprocessor circuits. Streptococci introduced into such a system are diluted, starved and progressively inactivated rather than amplified. They do not form the structured, self-sustaining biofilm communities characteristic of premise plumbing, and they are not organisms that water treatment is designed to control, because they are not expected to be present. Where streptococci are recovered from a healthcare water sample, the relevant transmission question is not how the organism reached the water from the environment, but how human-derived material reached the sample or the circuit.

Relevance in endoscopy and reprocessing

There is no documented instance of streptococcal infection transmitted to a patient through endoscope reprocessing water. The organisms are not waterborne in the operational sense, and the endoscopy literature on water-related transmission is dominated by Gram-negative non-fermenters and non-tuberculous mycobacteria rather than by Gram-positive cocci. That should be stated plainly, because it sets the correct level of alarm for a facility reviewing a positive result.

The genus is nonetheless relevant to reprocessing for a different reason. Flexible gastroscopes and bronchoscopes contact heavily colonised mucosal surfaces, and the material aspirated through their channels contains large numbers of oral and upper respiratory streptococci. Recovery of streptococci from a reprocessing circuit or from an endoscope channel sample can therefore indicate that patient-derived organic material has not been fully removed, which is a cleaning-efficacy question rather than a water-quality question. Because manual cleaning and channel brushing are the steps that carry the bulk of the bioburden reduction, a residual mucosal organism points first at those steps, at the adequacy of pre-cleaning at the point of use, and at whether the correct brush sizes and channel connectors are being used for the model in question.

Streptococci contribute little to established premise-plumbing biofilm and are readily inactivated by the high-level disinfectants in routine use at their normal contact conditions, so they present no challenge to the disinfection step itself. The practical concern is what happens after it. If a streptococcus is recovered from a rinse or channel sample of a scope that has completed a validated cycle, either the sample was contaminated during handling or the post-disinfection pathway is reintroducing human-derived material. Drying, transport and storage practice, hand hygiene and glove change discipline between the reprocessor and the storage cabinet, and the cleanliness of transport trays and cabinet interiors are the elements to examine. In CSD and dental settings the same logic applies to final rinse water for instruments contacting mucosa and to dental unit waterline outputs, where operator handling at the point of sampling is a frequent source.

Interpreting a detection

A streptococcal isolate from a water or final rinse sample should be read first as a sampling and handling signal, not as evidence that the water plant is colonised. The organism cannot maintain itself in treated water, so its presence indicates recent introduction of human-derived material. The three realistic pathways are contamination of the sample at the point of collection, contamination of the sampling port or tap, and carry-over of patient-derived material within the reprocessor circuit or the endoscope itself. Each has a distinct corrective action, and the investigation should distinguish between them before any change is contemplated to the water treatment train.

The first checks are procedural. Confirm who collected the sample and how: whether the vessel was held open near the face, whether a mask was worn, whether the port was disinfected and adequately flushed before collection, whether gloves were changed, and whether the sample was transported and held within the required time and temperature window. Confirm the identification, since a Gram-positive coccus reported to genus level only may on further work prove to be a micrococcus, an aerococcus or a coagulase-negative staphylococcus, with different implications. Review the total viable count from the same sample and the accompanying indicator results: a streptococcus in an otherwise compliant, low-count sample behaves very differently from one accompanied by an elevated count or a Gram-negative co-isolate, which suggests a genuine system problem rather than an incidental touch contaminant.

A single isolate at low count, in a sample with an otherwise normal profile, is normally resolved by repeat sampling under strict aseptic technique with a documented method. A trend is a different matter. Repeated recovery, recovery from more than one outlet or reprocessor, recovery at high count, or recovery accompanied by rising total viable counts indicates a persistent pathway and warrants review of manual cleaning and brushing records, reprocessor self-disinfection cycles, the condition and change interval of terminal filters, and the post-rinse handling and storage pathway. Escalation to the infection prevention team is appropriate where the isolate is a beta-haemolytic species such as S. pyogenes or S. agalactiae, where any patient has a clinically linked infection with a matching organism, or where the pattern persists after sampling technique has been corrected and verified. In that situation the affected reprocessor and the instruments processed on it should be quarantined pending investigation.

Antimicrobial resistance

Streptococcus pyogenes remains uniformly susceptible to penicillin, which is still the agent of choice, and no clinically resistant isolate has been reliably documented. Resistance to macrolides and lincosamides, however, is well documented and varies considerably by region and over time, which limits their use as empirical alternatives in penicillin-allergic patients. Macrolide resistance is mediated either by target-site methylation through erm genes, which also confers clindamycin resistance and may be inducible, or by active efflux through mef genes, which affects macrolides alone. The distinction matters clinically because clindamycin is used as an adjunct in severe invasive disease for its suppression of toxin synthesis, and inducible resistance must be excluded before it is relied upon.

Streptococcus pneumoniae shows reduced beta-lactam susceptibility through alterations in penicillin-binding proteins rather than beta-lactamase production, so beta-lactamase inhibitors confer no benefit and higher-dose or higher-affinity agents are the response. Macrolide and tetracycline resistance are also encountered, frequently together on mobile elements, and reduced fluoroquinolone susceptibility has emerged in some settings. Serotype distribution and resistance rates have both been shaped by conjugate vaccine programmes, with reductions in disease caused by vaccine serotypes offset in part by replacement with non-vaccine types.

Streptococcus agalactiae remains beta-lactam susceptible but macrolide and clindamycin resistance is common enough to require susceptibility testing when these agents are used for intrapartum prophylaxis in penicillin-allergic women, and laboratories are expected to test specifically for inducible clindamycin resistance in that context. Susceptibility testing is therefore indicated for all clinically significant isolates outside S. pyogenes. In the reprocessing context, antimicrobial resistance has no bearing on control: streptococci carry no biocide tolerance of note, have no spore stage, and are inactivated by high-level disinfectants and by thermal processes at ordinary parameters. Control depends on cleaning, aseptic handling and drying, not on disinfectant selection.