Active Trachoma Cases in the Solomon Islands Have Varied Polymicrobial Community Structures but Do Not Associate with Individual Non-Chlamydial Pathogens of the Eye.

BACKGROUND: Several non-chlamydial microbial pathogens are associated with clinical signs of active trachoma in trachoma-endemic communities with a low prevalence of ocular Chlamydia trachomatis (Ct) infection. In the Solomon Islands, the prevalence of Ct among children is low despite the prevalence of active trachoma being moderate. Therefore, we set out to investigate whether active trachoma was associated with a common non-chlamydial infection or with a dominant polymicrobial community dysbiosis in the Solomon Islands. METHODS: We studied DNA from conjunctival swabs collected from 257 Solomon Islanders with active trachoma and matched controls. Droplet digital PCR was used to test for pathogens suspected to be able to induce follicular conjunctivitis. Polymicrobial community diversity and composition were studied by sequencing of hypervariable regions of the 16S ribosomal ribonucleic acid gene in a subset of 54 cases and 53 controls. RESULTS: Although Ct was associated with active trachoma, the number of infections was low (cases, 3.9%; controls, 0.4%). Estimated prevalence (cases and controls, respectively) of each non-chlamydial infection was as follows: Staphylococcus aureus: 1.9 and 1.9%, Adenoviridae: 1.2 and 1.2%, coagulase-negative Staphylococcus: 5.8 and 4.3%, Haemophilus influenzae: 7.4 and 11.7%, Moraxella catarrhalis: 2.3 and 4.7%, and Streptococcus pneumoniae: 7.0 and 6.2%. There was no statistically significant association between the clinical signs of trachoma and the presence or load of any of the non-Ct infections that were assayed. Interindividual variations in the conjunctival microbiome were characterized by differences in the levels of Corynebacterium, Propionibacterium, Helicobacter, and Paracoccus, but diversity and relative abundance of these specific genera did not differ significantly between cases and controls. DISCUSSION: It is unlikely that the prevalent trachoma-like follicular conjunctivitis in this region of the Solomon Islands has a dominant bacterial etiology. Before implementing community-wide azithromycin distribution for trachoma, policy makers should consider that clinical signs of trachoma can be observed in the absence of any detectable azithromycin-susceptible organism

Low Prevalence of Conjunctival Infection with Chlamydia trachomatis in a Treatment-Naïve Trachoma-Endemic Region of the Solomon Islands

Trachoma is endemic in several Pacific Island states. Recent surveys across the Solomon Islands indicated that whilst trachomatous inflammation-follicular (TF) was present at levels warranting intervention, the prevalence of trachomatous trichiasis (TT) was low. We set out to determine the relationship between chlamydial infection and trachoma in this population. We conducted a population-based trachoma prevalence survey of 3674 individuals from two Solomon Islands provinces. Participants were examined for clinical signs of trachoma. Conjunctival swabs were collected from all children aged 1-9 years. We tested swabs for Chlamydia trachomatis (Ct) DNA using droplet digital PCR. Chlamydial DNA from positive swabs was enriched and sequenced for use in phylogenetic analysis. We observed a moderate prevalence of TF in children aged 1-9 years (n = 296/1135, 26.1%) but low prevalence of trachomatous inflammation-intense (TI) (n = 2/1135, 0.2%) and current Ct infection (n = 13/1002, 1.3%) in children aged 1-9 years, and TT in those aged 15+ years (n = 2/2061, 0.1%). Ten of 13 (76.9%) cases of infection were in persons with TF or TI (p = 0.0005). Sequence analysis of the Ct-positive samples yielded 5/13 (38%) complete (>95% coverage of reference) genome sequences, and 8/13 complete plasmid sequences. Complete sequences all aligned most closely to ocular serovar reference strains. The low prevalence of TT, TI and Ct infection that we observed are incongruent with the high proportion of children exhibiting signs of TF. TF is present at levels that apparently warrant intervention, but the scarcity of other signs of trachoma indicates the phenotype is mild and may not pose a significant public health threat. Our data suggest that, whilst conjunctival Ct infection appears to be present in the region, it is present at levels that are unlikely to be the dominant driving force for TF in the population. This could be one reason for the low prevalence of TT observed during the study

Relationship between the prevalence of conjunctival <i>C</i>. <i>trachomatis</i> infection (diagnosed by nucleic acid amplification test) and trachomatous inflammation—follicular (TF) in the total 0–9 year-old population or a subset of that group at the district level (n = 35 districts).

<p>Correlation coefficient (R) is 0.84.</p

Published age-specific trachomatous inflammation—follicular (TF) prevalence data in studies undertaken in districts with >10% TF in overall child population (dotted and dashed lines), compared to the same in Temotu, Rennell and Bellona, Solomon Islands, October-November 2013 (grey columns).

<p>Published age-specific trachomatous inflammation—follicular (TF) prevalence data in studies undertaken in districts with >10% TF in overall child population (dotted and dashed lines), compared to the same in Temotu, Rennell and Bellona, Solomon Islands, October-November 2013 (grey columns).</p

Comparison of unadjusted prevalence of trachomatous trichiasis (TT) in 15+ year olds, and trachomatous inflammation—follicular (TF) in 1–9 year-olds, in treatment-naïve trachoma-endemic EUs for which data have previously been published (n = 58), and in which the TF prevalence in 1–9 year-olds was 10–40%.

<p>Correlation coefficient (R) is 0.40 for this subset, but 0.77 if including studies from areas of any prevalence.</p

Oligonucleotides used in this study.

<p>Chlamydial targets adapted for ddPCR [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004863#pntd.0004863.ref023" target="_blank">23</a>,<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004863#pntd.0004863.ref024" target="_blank">24</a>] based on sequences from Pickett and colleagues [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004863#pntd.0004863.ref087" target="_blank">87</a>]. Endogenous control target adapted from Luo and colleagues [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004863#pntd.0004863.ref088" target="_blank">88</a>].</p

Age-specific prevalence (grey bars) and 95% confidence interval (arrows) of trachomatous inflammation—follicular (TF) in individuals aged 1–15 years, recorded during a trachoma survey of Temotu, Rennell and Bellona, Solomon Islands, October-November 2013.

<p>Age-specific prevalence (grey bars) and 95% confidence interval (arrows) of trachomatous inflammation—follicular (TF) in individuals aged 1–15 years, recorded during a trachoma survey of Temotu, Rennell and Bellona, Solomon Islands, October-November 2013.</p

Frequency of conjunctival <i>C</i>. <i>trachomatis</i> infection and active trachoma during a trachoma survey in Temotu, Rennell and Bellona, Solomon Islands, October-November 2013.

<p>Frequency of conjunctival <i>C</i>. <i>trachomatis</i> infection and active trachoma during a trachoma survey in Temotu, Rennell and Bellona, Solomon Islands, October-November 2013.</p

Sequencing parameters and results of BLASTn analysis of consensus sequence.

<p>Conjunctival <i>C</i>. <i>trachomatis</i> genomes obtained from Temotu, Rennell and Bellona, Solomon Islands, in October-November 2013.</p