Levels of a bacterium in the Ala Wai boat harbor had dropped to normal levels within a week and a half after a major sewage spill ended and during the time in which a Honolulu man ended up in the waters and later died, according to a University of Hawai'i research team.

Although it is not known how high the bacteria concentrations were when Oliver Johnson went into the waters on March 31, researchers say the results show the bacterium appears to be a normal part of the mix in and around the Ala Wai.

Johnson's death on April 6 had raised concerns about higher-than-normal bacteria counts resulting from the spill, which had started a week earlier.

"What I found comforting, under the conditions we sampled, is that we don't have a hotbed of high levels of vulnificus in the canal," said microecology assistant professor Grieg Steward, one of the researchers.

The UH team sampled for a group of bacteria called vibrio, of which one species causes cholera and another, Vibrio vulnificus, was implicated in Johnson's death.

The samples were taken April 10 and tested by a team comprising Steward, geochemistry professor Eric DeCarlo and Olivia Nigro, a graduate student in microbiology. They found that vibrio bacteria are normally found in and around the Ala Wai, and that the concentration drops as the water grows more salty near the sea. Vibrio bacteria prefer brackish water, Steward said.

The sewage spill, which started March 24 and continued for six days, was caused by the failure of a 42-inch pressurized city sewage main. Forty-eight million gallons of sewage was diverted into the Ala Wai Canal during that period, prompting bans on water activities in the canal and nearshore areas around its outflow to the sea.

State Department of Health warning signs remained posted at coastal areas for several days after the spill.

Johnson, 41, died six days after he went in the boat harbor's waters with a cut on his foot. He died of massive organ failure due to septic shock, from an infection of Vibrio vulnificus. He was more susceptible to the infection than most people because of an immune system compromised by chronic liver disease, said Dr. William W. Goodhue Jr., first deputy medical examiner for the city.

Goodhue said that while he was able to determine the cause of death, he has listed the manner of Johnson's death as undetermined, mainly because two key factors in the illness are still not clear and are under investigation by Honolulu detectives.

One is whether the wounds on Johnson's left foot, which allowed the bacteria to take hold, were accidental or inflicted by someone else. Another is how he got into the tainted Ala Wai waters — whether he was pushed, fell while fleeing someone or fell accidentally.

"There is no witness, to my knowledge," Goodhue said.

"Based on the data we have, there is no compelling evidence to favor one manner of death as opposed to another."

Both Goodhue and Steward said Johnson was more susceptible to the infection than normally healthy adults because alcoholic liver disease had weakened his immune system. And while it is possible that he had a greater chance of infection due to the sewage spill, it is possible to be infected even in normal conditions, Steward said.

"It is really rare for someone to get an infection with vulnificus like this, but they're always there. It is naturally an estuarine organism. It doesn't do as well in full-strength ocean water or in pure fresh water," he said.

Steward said vibrio is a group of bacteria of which four species are notable as problems for humans. One causes cholera, two are associated with poisoning from eating infected shellfish, and the fourth, Vibrio vulnificus, can cause severe infections, particularly in people with weakened immune systems. The bacteria are found in brackish water worldwide. Several people with challenged immune systems contracted Vibrio vulnificus infections in the floodwaters of Hurricane Katrina, and some died.

The U.S. Centers for Disease Control and Prevention issued this recommendation after Hurricane Katrina's flooding: "To prevent (vibrio) infections, persons with open wounds or broken skin should avoid contact with brackish water or seawater, especially if they have preexisting liver disease or other immunocompromising conditions. Injury prevention is especially important for persons in these high-risk populations. Healthy persons are at much lower risk for (vibrio) infection."

In the Ala Wai area, the levels of all vibrio species in samples found April 10 — 12 days after the sewage spill ended — were from 2 to 200 colony-forming units per 100 milliliters, about 3 ounces. Steward said water samples are placed on a growth medium and the number of bacterial colonies that result are counted to come up with these numbers.

That is roughly equivalent to levels found in Hawaiian waters in previous studies. A 1998 study by Roger Fujioka of the UH Water Resources Research Center found levels of 1 to 184 off south O'ahu.

Steward's team, in its report released yesterday, wrote: "Concentrations of vibrio species and Vibrio vulnificus in particular ... were not unusually elevated in the Ala Wai Canal or the Ala Wai Yacht Harbor relative to other estuarine and marine environments on April 10."

That does not mean that the Ala Wai Canal and waters downstream are safe places for swimming. Steward said he would avoid swimming or fully immersing oneself, and would wash with soap and fresh water immediately after being in the water.

"It's not great water, not ideal for recreation, but it's probably as good as it was" before the sewage spill, he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.