The recent deaths of a 15-year-old and three other workers at an iPhone plant in Shanghai highlight the challenges that Apple Inc. and its suppliers face to maintain worker safety and keep underage people out of factories.
In September, 15-year-old Shi Zhaokun began work at Pegatron's Shanghai assembly plant using an identification card that said he was 20. A month later, he died of pneumonia.
Labor groups said long working hours and crowded living conditions contributed to Shi's death.
Taiwan-based Pegatron on Wednesday confirmed that four workers died of illnesses recently at the Shanghai factory, which employs about 100,000 people.
Pegatron and Apple said their investigations indicated that the deaths weren't linked to work conditions.
In response to Shi's death, Apple last month sent independent medical experts from the U.S. and China to the Pegatron factory to conduct an investigation, Apple spokeswoman Carolyn Wu said. "While they have found no evidence of any link to working conditions there, we realize that is of little comfort to the families who have lost their loved ones," she said.
Apple declined to comment about employment of underage workers, although the company has long said it is diligent about enforcing age rules at its suppliers.
It was unclear how Shi — who, his family said, was pronounced healthy at a Pegatron checkup in September — ended up dying of acute pneumonia a month later.