Using milk leukocyte differentials for diagnosis of subclinical bovine mastitis – CORRIGENDUM

Abstract

The authors would like to apologise for a mistake in the above-mentioned article by Gonçalves et al. Checking the data, it was found that the position of false-positive and false-negative results were accidently reversed when calculating sensitivity and specificity.The following errors have been noted:On the first page, in the abstract:'When MC was considered the gold standard for mastitis diagnosis, the calculated diagnostic Se of the MLD was 65·4% (IC 95% = 57·4 to 72·8%) and the Sp was 79·3% (IC 95% = 71·4 to 85·7%).' Should read:'When MC was considered the gold standard for mastitis diagnosis, the calculated diagnostic Se of the MLD was 78·5% (IC 95% = 70·4 to 85·2%) and the Sp was 66·5% (IC 95% = 58·6 to 73·7%).'On page 313, in the second column:'When MC was considered the gold standard for mastitis diagnosis, the calculated diagnostic Se of the MLD was 65·4% (IC 95% = 57·4 to 72·8%) and the Sp was 79·3% (IC 95% = 71·4% to 85·7%). Using MC results as the 'gold standard,' Se and Sp of the categorical instrument readout results (healthy or infected) based upon cut-offs ranging from 1-12 are shown in Fig. 2. Sensitivity progressively increased from a minimum of 50·4% at a user setting of 1 to a maximum of 71·3% at a setting of 12 (Fig. 2). Specificity progressively decreased from a maximum of 86·7% at user setting 1 to 66·7% at setting 12 (Fig. 2).' Should read:'When MC was considered the gold standard for mastitis diagnosis, the calculated diagnostic Se of the MLD was 78·5% (IC 95% = 70·4 to 85·2%) and the Sp was 66·5% (IC 95% = 58·6 to 73·7%). Using MC results as the 'gold standard,' Se and Sp of the categorical instrument readout results (healthy or infected) based upon cut-offs ranging from 1-12 are shown in Fig. 2. Sensitivity progressively decreased from a maximum of 95·4% at a user setting of 1 to a minimum of 47·7% at a setting of 12 (Fig. 2). Specificity progressively increased from a minimum of 24·2% at user setting 1 to 84·5% at setting 12 (Fig. 2).'On page 314, In Figure 2, the sensitivity and specificity results were accidently reversed, since the position of false-positive and false-negative results were mistakenly allocated in the 2 × 2 contingency table used for calculations.

Relationships among quarter milk leukocyte proportions and cow and quarter-level variables under different intramammary infection statuses

“…In more recent reports, NEU proportions ranged between 6 and 50%, LYM proportions between 14 and 80%, and MAC proportions between 12 and 46% ( Rivas et al, 2001 ; Merle et al, 2007 ; Koess and Hamann, 2008 ; Schwarz et al, 2011b ). Interestingly, our observed distribution of white cells in milk from healthy quarters was similar to that recently described by Gonçalves et al (2017) . The main cell type for healthy quarters in our study was NEU (51.4%), followed by MAC (30.1%) and LYM (17.4%).…”

“…The main cell type for healthy quarters in our study was NEU (51.4%), followed by MAC (30.1%) and LYM (17.4%). In agreement, Gonçalves et al (2017) reported NEU, MAC, and LYM percentages in milk of culture negative udder quarters of 49.4, 28.9, and 17.7%, respectively.…”

“…Milk was collected following standard aseptic procedures ( National Mastitis Council, 1999 ) that included teat-end disinfection with alcohol and disposal of the first streams of milk. The device reader has programmable threshold levels on a scale of 1 to 18 that may be selected by the user, and different thresholds would result in higher sensitivity or higher specificity ( Godden et al, 2017 ; Gonçalves et al, 2017 ). The reported sensitivity and specificity for this technology at threshold level 7, using microbiological culture as a gold standard, were 65.4% and 79.3%, respectively ( Gonçalves et al, 2017 ).…”

“…The cassette was immediately loaded into the automated reading device, using the research mode (threshold level 6) that required about 15 min per cassette and offered increased accuracy for the differentials. The device uses a fluorescence microscopy imaging system taking images to identify and count lymphocytes ( LYM ), neutrophils ( NEU ), and macrophages ( MAC ; Godden et al, 2017 ; Gonçalves et al, 2017 ). Results are provided as total leukocyte counts ( TLC ) and as absolute values for each cell type (NEU, LYM, and MAC).…”

“…The use of a milk leukocyte differential ( MLD ) test, providing the proportions of specific leukocytes in milk, has been proposed as a complement to SCC to assess the presence and the severity of IMI ( Dohoo et al, 1981 ; Leitner et al, 2003 ; Godden et al, 2017 ). Moreover, in recent studies, MLD has been suggested as a screening option for IMI in selective dry cow therapy and fresh cow assessment ( Godden et al, 2017 ; Gonçalves et al, 2017 ). According to a recent study ( Godden et al, 2017 ), costs for the MLD test are approximately $18,000 for the reader, $5.00 per cow for the cassette, in addition to the cost of labor for the sampling and the analysis procedures.…”