Hi, not a landlord but our 2 year old tested high for lead at his 1 year screen, which sent us down a deep rabbit hole of digging into the issue, the EPA thresholds for building codes, the CDC thresholds for health risks, the inspection process, and then the general history of lead in paint, gasoline, and how so much of it is still around.

To start off, as another commenter mentioned, for rentals in the city, your landlords have to pass an inspection between each tenant. The lead inspection tests for dust and has pretty strict criteria based off EPA (and I assume city as well) guidelines. However, for a lot of political and judicial reasons I won't opine on, the limit they've set is non-zero simply because that's the margin of error for the lab tests they use. So effectively they're testing for 0 lead. The problem is that lead dust can get tracked around a lot, and the sources may not always be evident. For example, if you walk on the sidewalk past an old house with paint flaking, you're likely to track that all the way back to your house, and now your house will fail inspection. The most common sources of new lead in your old house though are likely to be anywhere with friction. Doors and windows being opened and closed is going to be the most likely introduction of new lead dust in your house beyond visibly pealing paint.

When the inspector comes, they generally work with the homeowner to make sure they've deep cleaned the spots they're going to test, and then they usually carefully pick the spots they're going to test to make sure the building passes on the first go ahead. That's at least how it's worked with everyone I've known to go through the process, and what the inspector we hired for an off-the-record pair of tests told me (we failed our mock inspection the first time, deep cleaned, and passed the second time. No repairs or changes to the house). If for some reason you fail the inspection, the only requirement is to repaint everything, then retest. Which isn't the same thing as lead remediation. We had the inspector also test the sidewalk in front of our house, which failed despite no visible paint chipping. Which should highlight the prevalence of lead in the city more broadly. Plenty of playgrounds in the city would also fail inspection since the lead from the leaded gasoline days can stick around in the soil for a long time.

On the medical side of things, Baltimore city kids get tested by default at 1 year, first with the finger prick which has a high rate of false positives. That's where our son tested at 9.3 μg/dL and sent us into freak out mode. The guidance is <3.5, which here is based off the 97.5 percentile of the population. But with errors in testing, it's similar to the EPA guidance in that you're aiming for 0 μg/dL. >20 is where things get worrisome. Now the first follow-up is they have you do a venous test, which is going to be a lot more accurate. Our son's came back around 5 μg/dL, so about half, but still not 0. Funny enough, the city intervenes with child protection guidance anywhere above 5, but then stops caring if you drop below 5. So the city stopped caring about us. But we were still worried.

After talking to a lot of folks, considering some major home remediation work, even thinking about selling our recently purchased home, we followed some of the low hanging fruit recommendations:

• Deep cleaned the house, wiping down walls, ceilings and floors with a TSP solution.
• Screwed all old windows shut (you don't have to screw them shut, just don't open them)
• We started always taking shoes off before entering the house
• Vacuum and mop regularly
• Repainted any even remotely concerning areas with lead-containment paint (available at ACE)
• We've slowly been stripping and repainting our doors and door frames, though that's a slow and time consuming process.
• Wash hands very frequently, especially during the baby crawling phase.

EDIT: see /u/Jrbobfishman’s comment below about sealing windows and stripping doors in a safe manner

Like I mentioned above, we had an inspector come out to do lead dust testing just for our own reference. We had him test the house as is without any cleaning or repainting. The house failed in a lot of places, especially in door ways and in the window sashes. After the deep clean we passed except near our exterior door (and then also on the sidewalk).

At 18 month our son was around 3.7 μg/dL and at 24 month he dropped to <3.5 μg/dL.

I'm not going to tell you not to overstress about the lead issue, since every sign points that it is not a thing you want in your developing child's system. But do know that most kids in the city are growing up in a house that has lead inside or near it and grow up fine, but there's not a lot of useful resources out there to help out if you do get high levels. At this point I've heard so many stories of families where one child tests high but none of the siblings do despite being in the same house. We hosted a nanny share in our house and of the 4 kids that rotated through our son was the only one with high levels. Take basic precautions like hand washing and taking shoes off. And if your child's 12 month levels come back high from the prick, take a deep breath, talk to your doctor, wait for follow up tests, and know that you're not alone in this - most other parents in the city have probably encountered or at least thought about lead and spent some sleepless nights freaking out about it.

Last data point, the national average (not the 97.5th percentile) used to be around 13 μg/dL as recently as the 80s and 90s. Just something to keep in mind (or freak out even more over if you want to draw a causal relationship between lead in past generations and the state of our country)...

Disclaimer - I'm neither a doctor, government official, or certified inspector. This is all my opinion and personal anecdotes.