The key ingredients for an infectious disease outbreak are no secret: people with immune systems that have been weakened by stress and poor nutrition, crammed into close quarters with one another and denied basic hygiene and health care , for extended periods of time. That’s why diseases like cholera, dysentery and tuberculosis have long thrived in refugee camps and prisons and among soldiers during wartime.

So federal officials should not be surprised that migrant detention centers along the nation’s southern border have become hotbeds of communicable diseases — with multiple outbreaks of scabies, shingles, lice, mumps, chickenpox and flu logged this year and last. As the Office of Inspector General noted in a July report, these facilities are dangerously overcrowded. Detainees there have not been provided with adequate nutrition, sanitation or health care. And many of them are being held for weeks or months in quarters designed for a 72-hour stay.

The report describes horrendous conditions: 88 people crammed into a room meant for 41, detainees forced to go months without a shower or a change of clothes, young children covered in filth for weeks on end. At least six children have died from communicable diseases in these facilities in the past two years.

At least three of those deaths were related , in part, to flu. Which makes all the more confounding reports from CNBC and other outlets last week that immigration officials have no plans to vaccinate detainees before the coming flu season.