This story strikes me as a deeply Junji Ito type of horror, particularly the kind featured in his anthologies- it's never explained exactly what the balloons are, or where they came from, or even why they're there (though plenty can be inferred). The implications with that last scene are, as a certain scientist Salarian might say, unpleasant. What a creepy little bow to top it all off with.
It's one of my favorite types of horror, and made me shudder even before the story came to an end. Bravo.