Response: Variability in the prevalence of Chlamydophila psittaci infection in patients with OAML

We thank Drs Ponzoni et al for their interest in our review on extranodal marginal zone lymphoma of the ocular adnexa (OAML) and would like to express our point of view regarding the comments the authors are raising on the association between Chlamydophila psittaci (Cp) and OAML. As illustrated in our review, we indeed acknowledge the existing evidence supporting this association in certain but not all geographical areas as well as the epidemiologic and scientific approaches the authors have undertaken.^1,2  However, there is convincing evidence in the literature that this association is not as prevalent as indicated by the 2 series from Italy and Korea, which reported a prevalence of Cp infection in approximately 80% of OAML.^1,3  In fact, there appears to be considerable geographic variability in the prevalence of Cp infection in patients with OAML worldwide, with a wide range from 0% to 80%. The most heterogeneous data regarding the association between OAML and Cp infection have been reported from an international multicenter study, showing striking geographic variability even within the same countries, with an overall prevalence of Cp in only 22% of 195 OAML patients.⁴  Of note, the authors conducted 3 independent polymerase chain reaction (PCR) amplifications identical to the approach previously described by Ferreri et al, along with double-blind investigations performed in an independent laboratory, thus minimizing the potential for methodologic bias. Furthermore, in our analysis of OAML from South Florida, Cp could not be detected by 2 different PCR methodologies in any of the analyzed specimens^5,6 ; however, using the same PCR approaches, Cp was detected in the Italian positive control specimen kindly provided by Drs Ferreri and Ponzoni.⁵  Finally, a substantial body of evidence has been accumulated from 10 series including more than 250 patients from different geographic areas worldwide, the largest of which originates from our own institution,⁵  showing no association between OAML and Cp infection. Comparison of the materials and methods used to extract and detect Cp DNA in tissue samples among different studies reveals similar approaches including multiplex touchdown enzyme time-release PCR on fresh or paraffin-embedded fixed tissues. While methodologic differences and confounding factors such as the use of antibiotics may account for some of the observed discordant results, it is extremely unlikely that the apparent lack of an association between Cp and OAML can be entirely attributed to the influence of such biases. Although Ponzoni et al mention that the use of antibiotics may decrease PCR sensitivity for Cp detection, none of our patients received antibiotic therapy. Our patients, as well as many others reported in the literature as having no association with Cp, also differ epidemiologically from the Italian OAML patients in that only the latter often resided in rural areas, reported a history of chronic conjunctivitis and prolonged contact with household animals and were found to have an association with this bacteria. Of interest, Ponzoni et al recently demonstrated both viability and infectivity of Cp in conjunctival swabs of patients with not only conjunctival OAML, but also in cases of orbital soft tissue and lacrimal gland OAML. This observation, which according to the authors fulfills one of the Koch postulates on association of bacteria with disease (Table 1), actually raises the question of whether this association is indeed direct, since presence of bacteria in the conjunctiva might contribute to conjunctival OAML but does not explain development of lymphoma in other orbital tissues without simultaneous evidence of a conjunctival lymphomatous process. Furthermore, careful evaluation of the other Koch postulates raises further questions on the direct pathogenic association between Cp and OAML. As a matter of fact, Cp is not detected in all cases of OAML but has been reported in some control patients, which is not in keeping with the Koch postulates. Lastly, there are currently no experimental data that fulfill the third Koch postulate, requiring demonstration of the ability of the in vitro grown bacteria to induce disease (lymphoma) anew, and fourth Koch postulate (shown in Table 1) that would thus confirm the pathogenic role of Cp in OAML.

In conclusion, although epidemiologic data from some geographic regions, including Italy, suggest an association between Cp and OAML, the current evidence does not support a universal association, much less a causal relationship in the majority of patients affected with this disease. We agree with Ponzoni et al on the importance of methodologically rigorous clinical studies addressing these open questions and are awaiting the results of the IELSG27 international prospective study with great interest.