Abstract:
BACKGROUND : Stool samples submitted for diagnostic testing represent a proportion of diarrhoeal cases seeking
healthcare, and an even smaller proportion of diarrhoeal cases in the community. Despite this, surveillance relies
heavily on these laboratory results. This study described diarrhoeal diagnostic practices and aetiological agents of
diarrhoea in patients admitted to three South African public hospitals in order to understand biases in surveillance
data, and inform guidelines, diagnostic and laboratory practices to improve clinical management.
METHODS : A doctors’ survey was conducted to determine sample submission, diarrhoeal treatment and barriers to
submitting samples for testing. Results for all samples submitted for routine diagnostics were obtained from the NHLS
Central Data Warehouse. An enhanced surveillance study enrolled patients with acute diarrhoea at the same hospitals
over the same period. Differences between routine culture results and molecular testing from the surveillance study
were described.
RESULTS : Stool samples were seldom submitted for diagnostic testing (median of 10% of admitted cases). Current
diagnostic guidelines were not useful, hence most doctors (75.1%) relied on their own clinical judgement or judgement
of a senior clinician. Although most doctors (90.3%) agreed that diagnostics were helpful for clinical management,
they reported patients being unwilling to provide samples and long laboratory turnaround times. Routine
diagnostic data represent cases with chronic diarrhoea and dysentery since doctors are most likely to submit specimens
for these cases. Pathogen yield (number of pathogens detected for samples tested for specific pathogens)
was significantly higher in the surveillance study, which used molecular methods, than through routine diagnostic
services (73.3% versus 8.2%, p < 0.001), including for viruses (48.9% versus 2.6%, p < 0.001), bacteria (40.1% versus 2.2%,
p < 0.001) and parasites (16.2% versus 3.6%, p < 0.001). Despite viruses being commonly detected in the surveillance
study, viral testing was seldom requested in routine diagnostic investigations.
CONCLUSIONS : Comprehensive diagnostic and treatment guidelines are required for diarrhoeal diseases. These guidelines
should be informed by local epidemiological data, where diagnostic testing is reserved for cases most likely to
benefit from specific treatment. Optimisation of current diagnostic processes and methods are required for these
cases, specifically in terms of minimising turnaround times while maximising diagnostic acumen.
