NEW DELHI: India's foreign ministry confirmed on Thursday that 13 of its nationals had tested positive for the Zika virus in Singapore, after an outbreak of the mosquito-borne disease that at first affected three dozen workers on a construction site. 'According to our mission in Singapore 13 Indian nationals have tested positive for Zika in Singapore,' Vikas Swarup, spokesman for the Ministry of External Affairs, said in response to a Reuters inquiry. US health officials have concluded that Zika infections in pregnant women can cause microcephaly, a birth defect marked by small head size that can lead to severe developmental problems in babies.