Exploring the applicability of the California Mastitis Test to detect clinical and subclinical mastitis in milk from HIV-infected women.

摘要

Background. Mastitis in HIV-infected mothers is a risk factor for mother-to-child transmission (MTCT) of human immunodeficiency virus (HIV)-1, possibly as a result of higher milk viral load. While clinical mastitis is symptomatic, subclinical mastitis can only be detected by analyzing breast milk. A test that is quick, inexpensive, and reliable which could be used at the patient's side would provide immediate and important feedback regarding this condition.; Objectives. This thesis project investigated whether the California Mastitis Test, which was originally developed by veterinarians for use in dairy herds to screen for high cell counts, could be used to detect subclinical mastitis in human milk. This project also investigated whether there was a relationship between milk cell count and sodium, both signs of increased mammary permeability, and HIV-1 viral load in milk. If such a relationship existed, the CMT could then be recommended as an indirect screening tool for high viral counts in milk.; Design and methods. Validity of the CMT was tested using the direct microscopic somatic cell count (DMSCC) in 236 cross-sectional milk samples from HIV-positive breastfeeding mothers in Lusaka, Zambia, ranging from 1 week to 24 months postpartum. Samples containing extra volume were also tested for electrical conductivity, as a field-based proxy measure of major milk ions including sodium, using a portable veterinary milk conductivity meter. Sodium levels and HIV-1 RNA were measured in all 4-month postpartum samples that were tested for the CMT.; To confirm the phenomenon of high milk viral load in the presence of subclinical mastitis, we compared the mean milk viral load in samples with normal sodium levels versus those with elevated sodium in a group of 110 milk samples at 1 month postpartum that were not associated with any signs or symptoms of mastitis.; Results. Mean total cell counts in each CMT agglutination category as determined by DMSCC were significantly different from one another (P .01). In addition, human milk total cell counts significantly and positively correlated with sodium levels (r = .389, P = .006) and electrical conductivity (r = .649, P .001). In 4-month postpartum samples, sodium concentration correlated significantly with viral load (r = .291, P = .05), while there was a tendency for electrical conductivity to correlate with HIV-1 RNA (r = .331, P = .107). However, no correlation was found between milk viral load and cell count.; In the 1-month postpartum samples, there was a significant difference in the mean HIV viral load of samples with elevated sodium concentrations compared with samples having normal sodium levels (P .001).; Conclusions. This study validates the CMT as a reliable tool to screen for high cell counts in human milk; however because cell count and milk viral load were not associated, we are unable to recommend this method for indirect screening of high HIV viral load in milk. Since the ionic components of milk, as measured by sodium concentrations and electrical conductivity, are related to viral load, rapid tests for these milk components merit further investigation. Moreover, we confirmed that high viral loads are present during increased mammary permeability as measured by sodium levels when there is no evidence of clinical mastitis; therefore, we encourage efforts to reduce viral load in milk, such as antiretroviral therapy during lactation, in all HIV-infected breastfeeding mothers.