Reply to “Scabies Treatment Failure: Beyond Permethrin and Plastic Bags”

To the Editor,

We thank Dr. Gupta for the thorough reading and commentary on our article “Scabies Management Outcomes: Identification of Risk Factors for Treatment Success or Failure” recently published in Dermatology Practical & Conceptual [1].

We fully agree that self-reported questionnaires are subject to recall bias. This has already been discussed in our article, as also mentioned by Dr. Gupta. Nevertheless, recall bias was limited by two strategies. First, only the last treatment episode was recorded, i.e. participants only reported on the treatment they could most easily remember. Second, the questionnaire was filled out 2 to 6 weeks after completion of scabies treatment. This is a relatively short time period, which makes it more likely that correct information was noted.

As described in our method section, the categorization of “success” and “failure” was based on thoroughly performed dermatoscopy and microscopy of skin scrapings. Patients were only considered “failure”, if the diagnosis of scabies was established. That means a mite and/or feces and/or eggs was/were identified. Cure of scabies, and therefore classification as “success”, was defined by absence of fresh lesions combined with absence of mites and/or feces and/or eggs in remaining healing lesions.

Regarding the third point, the small size of the study cohort and its subgroups is a limitation, but this has also already been described in our text. In addition, the resistance of scabies mites to permethrin was first described by Riebenbauer et al. in November 2023 [2]. At that time, our study had already been completed and to date, laboratory confirmation of drug resistance is still far from being a routine procedure. Furthermore, Riebenbauer et al. showed that permethrin treatment can be successful even if the identified mutation is present [2].

We thank Dr. Gupta for agreeing with our discussed statement with his fourth point, that “it is possible that patients in the failure group follow treatment guidelines less carefully in general” and that “consequently, the single de-contamination measure itself might not be of the utmost importance, but a general willingness to follow the recommendations would be needed” [1]. This could also apply to the use of disinfectants.

Finally, other limitations of our work include that no information was collected about the total number of treatments or the time between onset of symptoms and first treatment. However, this was repeatably discussed in our publication. Socioeconomic factors were assessed and reported. The number of household members, the number of children and the mean age of children did not differ between the success and failure group. When asking about the suspected location of transmission, a distinction was made between “workplace” and “workplace (professional nursing)”. In addition, information on the highest education qualification of participants was collected. Aussy et al. also observed no differences in occupational status, household size and/or presence of children when investigating risk factors for treatment failure of scabies in France [3]. Sanei-Dehkordi did not analyze risk factors for treatment failure [4].

In summary, we agree with Dr. Gupta that our study has several limitations, all of which have already been discussed in our publication.