Acute rheumatic fever (ARF) is the most common cause of acquired heart disease in children worldwide in low resource settings (1, 2). Rates of ARF in Australian Aboriginal and Torres Strait Islander peoples (hereafter respectfully referred to as Indigenous) are amongst the highest reported in the world, at 374–508 per 100,000 aged 5–15 years (3–5). The most serious sequelae of ARF, rheumatic heart disease (RHD), occurs in 42%–60% of people with a prior history of ARF (3–6). Indigenous populations in Northern Australia have the highest reported rates of mortality from ARF or RHD worldwide (23.8 per 100,000) (3).

ARF is an autoimmune-mediated response that typically occurs 2–3 weeks after a group A streptococcal (GAS) throat infection (pharyngitis) or skin infection (impetigo) (7). In remote-living Australian Indigenous children with high RHD rates, GAS skin infections are endemic (8) whilst pharyngitis burden is uncommon (9). The reported incidence of sore throat is low at approximately 8 episodes/100 children/year [95% confidence interval (CI), 4–15 episodes per 100 person-years], and for symptomatic GAS pharyngitis, the reported incidence density is 0 (10). In contrast, a small study of 151 children with ARF found that 25% of remote-living Indigenous children had a recent sore throat preceding ARF diagnosis (11). Anecdotally, clinicians have reported that tonsillar hypertrophy (large/swollen tonsils) and sore throat presentations appear to be uncommon in Australian Indigenous children, compared to non-Indigenous Australian children.

Other research studies conducted by this team document the concurrent burden of GAS throat and skin infections in Australian Indigenous populations and assess the hypothesis that Australian Indigenous children do not commonly report sore throat or present with large tonsils (12). Most of the literature reporting on tonsil size in children is in the context of anthropometrics and sleep-disordered breathing, and preoperative clinical decision-making for tonsillectomies in clinical/hospital settings (13). Akcay and colleagues (14) developed a tonsil size distribution curve (via physical examination and grading) from 1,784 school children living in the city of Denizli, Turkey (14). Tonsil size distribution in Australian urban or remote-living children has not been documented previously. Further, using a photograph to illustrate tonsil size and hypertrophy has not been previously trialed in children, although some research has been conducted with adults (15). Medical photography can be a useful clinical tool that increases documentation, and improves both doctor-patient and inter-provider communication in remote Telehealth consultation (16). We developed a protocol for photography of the tonsils that could be used in research studies in remote settings as part of GAS pharyngitis assessments. Using this protocol, the project aimed to develop a standardised set of tonsil photographs to determine tonsil size distribution from an urban population of healthy children, to later compare with those collected from remote Indigenous children. The secondary aims were to document the presence of sore throat symptoms in participants, and where feasible, assess for the presence of GAS in the throat using a Rapid Antigen Detection Test (RADT). The secondary aims were not essential to the project but were included to enhance the participants' interaction with public science activities (described further in the methods).

This is the first study to our knowledge to recruit children at a public science event, develop a set of standardised tonsil photographs, and assess tonsillar size using photographs in lieu of the assessments typically used for real-time clinical assessment. Further, we have included comparative assessments from two clinicians of each of the available photographs to validate this innovative method. This study was feasible at a public science event and has clinical implications globally for improving comparative assessments of pharyngitis in children aged 3–15 years. This approach may have future applications in helping to improve pharyngitis assessment in remote contexts, where physicians are not always available and immediate access to assessments by clinicians or ear, nose and throat specialists may be limited.

Our results demonstrate moderate agreement between clinicians in grading tonsil size using photographs and the Brodsky Grading Scale for Tonsillar Hypertrophy. However, there was limited interrater reliability for signs of infection (swelling, redness, pus). Improvements to photo quality and therefore interrater reliability may be achievable using a single, trained clinical photographer as found in many tertiary hospitals. However, generally situations that require the use of digital images are those in which there are fewest resources and minimally trained clinicians or parents provide images that are captured, stored, and forwarded for assessment by a doctor who may be thousands of kilometres away. As such, in these situations having a single highly trained photographer may not be possible. Hence, these standardised tonsil photographs may be useful for assessing tonsillar size via telehealth, in assessing change in tonsillar size between presentations, in research or in primary prevention of ARF where clinical resources are limited. We will compare this standardised set from urban children with another study of remote living children at high risk of ARF and RHD (12).

Askarian and colleagues (15) developed a novel detection methodology for GAS throat infection utilising a smartphone, add-on gadget and post-processing algorithm, in adults, and reported an accuracy of 94% for GAS throat infection detection (15). This technology and method had not been published at the time of data collection for this study, and is limited by not including children as childhood is the primary age when pharyngitis presents. Further advancements in this type of methodology in children could be considered in future research.

The tonsillar size we observed in urban children in Australia were larger than international studies (14). Most tonsils were rated as grade 1, followed by 2 and 3, whilst grade 0 and 4 were infrequent. Akcay and colleagues using physical examination of tonsil size, identified the majority (63%) of tonsils as grade 1, followed by 2 (28%), but 3 and 4 occurred infrequently (2% and <1% respectively), in a similar age bracket to our cohort (4–17 years old) (14). The authors did not use a grade 0 rating, so we are unable to compare these results. Their study had a larger sample size (>1,000 children) than this study. The authors do not report on the average age of the cohort but note that tonsil size peaked at ages 4–8 years, with grade 4 tonsils observed only in six and seven-year-old children, which was the average age of our cohort. A limitation of our study was that real-time physical examination/grading of tonsils was not completed, so cannot be correlated with grades determined from the clinicians' assessment of these photographs. Future studies will benefit from documenting and comparing tonsil size via both methods.

In this urban population at low risk of developing ARF, we found that few (<1%) had evidence of throat infection with only two RADTs for GAS found to be positive. Low numbers of positive RADTs and grade 4 tonsil sizes were anticipated given that the data was collected from a well, community-based cohort. The two positive RADT results were from participants who did not report a sore throat or other symptoms of infection. As the children had no symptoms of infection, the corresponding tonsillar photographs were not individually reported. It is possible that the positive tests were detecting GAS carriage, however the RADT is validated only for detecting GAS pharyngitis and not carriage—and therefore would not usually have been performed in an asymptomatic child. As throat swabs for GAS culture were not collected, confirmation of GAS identification in the throat remains a limitation of the study, and these two positive tests may have been false positives. Future prospective studies in remote Indigenous cohorts will collect culture and serological tests to assess the presence of active or previous GAS infection and potential GAS carriage (12). Analysis of the subset of tonsillar photographs from children who presented with sore throats was not performed but could be considered in future studies.

Other limitations of the study included the rapid pace of data collection which contributed to varying rates of participation (and therefore denominators) in each of the three main data collection activities and results. Multiple research staff, while trained in the standard operating procures, may have contributed to the varying quality of photographs, with some staff more familiar with interacting with children than others. While the public science setting of this initial study allowed for rapid completion of data collection, across a broad cross-section of healthy children, more regimented data collection in future studies could improve the quality of photographs and interrater reliability. Observationally it was noted that for some children a photograph with a clear view to the back of the throat was not possible to collect (usually due to obstruction by the tongue or the child being unable to open their mouth wide enough despite prompting). This is likely to have contributed to the portion of photographs deemed not able to be graded by the independent clinicians. The sample size of over 400 participants in an urban setting public science event may not be generalisable to other populations and clinical settings, and further studies are needed. Further, tonsillar hypertrophy is not diagnostic of GAS pharyngitis and, thus, the photographs should not be used alone in diagnosis. Future studies could compare this set of photographs from healthy children to those with GAS pharyngitis to better validate and assess the clinical utility of this set of tonsillar photographs.

We report the first collection of tonsil photographs in children globally. We successfully assessed tonsil size using a standardised method carried out within an urban-living cohort of healthy children in Australia. The learnings from this study will be applied in future studies and these results compared to those from future studies involving children living in remote Indigenous communities in Australia and other populations globally at high risk of rheumatic fever. This will help progress our research towards improved primary prevention strategies to end RHD in remote-living Indigenous populations of Australia and align with the WHO resolution to prioritise rheumatic fever and RHD as global health problems (25).