Table 2. Reported negative cases of milk samples.

Publication	Number of subjects	Retested milk samples	Infected infant	Infant breastfed	Observations
Han et al.71	1	N/A	Yes	Yes	High viral load in infant’s tests. Viral presence in all samples (blood, urine, stool). Viral persistence in stool after symptoms cessation.
Kalafat et al.76	1	N/A	No	N/S	Pregnant woman with severe respiratory symptoms admitted to the ICU and intubated. Negative placental, cord blood and milk samples. Neonatal swab was negative.
Mao et al.48	1	Yes	Yes	Yes	Viral persistence in stool and nasopharyngeal swab after symptoms cessation. Presumed household horizontal transmission.
Peng et al.49	1	Yes	No	No	Besides maternal nasopharyngeal swab all other maternal and neonatal samples were negative. Breast milk samples negative on 7 different tests.
Xiong et al.60	1	No	No	N/S	Negative samples from milk, cervical secretion, amniotic fluid, rectal swab.
Chen et al.61	3	N/S	No	N/S	Milk samples from 3 women infected with SARS-CoV-2 yielded negative results.
Piersiglli et al.71	1	N/S	Yes	No, expressed milk used instead	Horizontally acquired COVID-19 in a preterm neonate with unspecific symptomatology.
De Socio et al.68	1	No	No	Yes	Apart from maternal nasopharyngeal swab all sample were negative.
Perrone et al.69	1	Yes	No	Yes	Milk samples negative on 3 occasions.
Zaghal et al.75	1	No	No	Yes	Neonatal nasopharyngeal swab was negative on 3 occasions.
Dong et al.62	1	Yes	Yes	Yes	IgG and IgA antibodies discovered in the breast milk.
Deng et al.63	6	N/S	No	N/S	Negative neonatal samples.
Lang et al.64	1	No	No	N/S	Apart from maternal nasopharyngeal swab, all other maternal and neonatal samples were negative.
Wang et al.65	1	No	N/S	N/S	Consistently positive maternal stool sample. Other maternal samples (milk, nasopharyngeal swab) were negative.
Chen et al.66	6	No	No	N/S	Apart from maternal NPS all other maternal and neonatal samples were negative.
Cui et al.67	1	Yes	Yes	Yes	Severe symptomatology in a 55 days old infant. Infant positive tests persist in stool samples and anal swabs after symptoms cessation. Maternal positive tests in anal swabs.
Dong et al.50	1	No	No	No	Negative maternal milk and vaginal samples. Consistent negative neonatal nasopharyngeal swab on 4 different occasions. IgM antibodies found in the neonate’s serum, thus potentially suggesting for in-utero vertical transmission.
Fan et al.51	2	Yes	No	No	Apart from maternal nasopharyngeal swabs, all other samples, both maternal and neonatal, were negative.
Kam et al.74	1	No	Yes	Yes	Persistently positive infant’s nasopharyngeal swab tests until day 16. First day-viremia corroborated with a fever episode. Initially stool samples were negative, later turned positive.
Li et al.52	1	Yes	No	N/S	Apart from maternal nasopharyngeal swabs, all other samples, both maternal and neonatal, were negative.
Salvatori et al.70	2	No	Yes	Yes	Neonatal nasopharyngeal swabs positive, presumed horizontal transmission; Breastfeeding allowed.
Liu et al.53	10	No	No	No	Apart from maternal nasopharyngeal swabs, all other samples, both maternal and neonatal, were negative.
Wang et al.54	1	No	Yes	No	Neonate tested positive 36 hours after birth. Cord blood, breast millk and placental samples yielded negative results. Vertical transmission can’t be ruled out.
Yu at al.55	1	Yes	Yes	Yes	Apart from nasopharyngeal swab, all other maternal samples were negative. Nasopharyngeal and stool samples consistently tested positive in the case of the infant. No SARS-CoV-2 RNA was found in the breast milk. However, IgG antibodies were detected, with a potential benefic impact for the infant’s development.
Lei at al.56	4	N/S	No	N/S	No other maternal positive sample apart from nasopharyngeal swabs. No neonatal samples were positive.
Yan et al.57	116 infants in total	No	No	N/S	86/86 neonates tested for COVID-19 had negative results. 12/12 milk samples were negative. 6/6 vaginal samples were negative. 10/10 amniotic fluid and cord blood samples were negative.
Marin et al.72	7	N/S	No	Yes	No infant was tested positive for SARS-CoV-2. All mother-infant dyads were allowed skin-to-skin contact.
Peng et al.58	25	Yes	No	Majority chose expressing milk	No milk sample tested positive. No vertical transmission via breast milk reported.
Gao et al.59	12	Yes	No	No	No viral shedding in maternal milk or cord blood. IgG and IgM detected in 3 breast milk samples.
Pace et al.78	37	No	N/S	N/S	37 milk samples tested negative for viral RNA. 1 positive breast swab turned negative after washing the skin; IgG and IgA antibodies found in milk samples.